Singapore has one of the lowest scores in the democracy index among OECD developed countries. It has always been.
Why is that?
It scores 6.22, a flawed democracy.
It scores low on "Electoral Process and Pluralism" (4.83) and "Political Participation"(4.44). Essentially the politics of Singapore are utterly dominated by the People's Action Party. The PAP uses legal action to erode the finances of opposition parties and politicians, with some becoming bankrupt.
It is widely believed that districts that vote for Opposition candidates will receive less support in housing programmes. And there is strict control of the press with newspapers or broadcasters that are critical of the government facing lawsuits that leave them bankrupt or unemployable.
The result is a system that is highly regulated and law-abiding, but in which there is a de-facto one party system and little democracy. Hence there is little plurality and little real political participation.
(The examples above are from the Wikipedia page on the politics of Singapore)
This answer was edited based on the - Singapore: Freedom in the World 2020 Country Report. Some factors affecting its scores are:
Unbalanced political systems and legislative representatives in the parliament:
Singapore is a parliamentary representative democratic republic with a (in theory) multi-party system. Since 1965, Singapore's policy has been dominated by the People's Action Party (PAP). Therefore, Singapore is classified as a one-party state by critics.
In the 2015 elections, the PAP secured nearly 70 percent of the popular vote and 83 of the 89 elected seats. The largest opposition group, the Workers’ Party (WP), retained the six elected seats it had won in 2011, but lost a seat it won in a 2013 by-election. Three compensatory seats were awarded to the opposition to achieve the minimum of nine.
Elections are largely free of fraud and other such irregularities, but they are unfair due to the advantages enjoyed by the incumbent party, including a progovernment media sector, the GRC (Group Representation Constituencies) system, high financial barriers** to electoral candidacy, and legal restrictions on free speech.
Influence of money and big businesses:
The corporatist structure of the economy creates dense ties between business and political elites that have been criticized as oligarchic in nature. These networks contribute to the PAP’s political dominance.
Singapore has been lauded for its lack of bribery and corruption. However, its corporatist economic structure entails close collaboration between the public and private sectors that may produce conflicts of interest. Lawmakers often serve on the boards of private companies, for example. The current prime minister’s wife is the chief executive of Temasek Holdings, a government-linked corporation and sovereign wealth fund; the relationship has drawn accusations of nepotism and cronyism.
Lack of openness and transparency in government operations:
The government provides limited transparency on its operations. The Singapore Public Sector Outcome Review is published every two years and includes metrics on the functioning of the bureaucracy; regular audits of public-sector financial processes are also made accessible to the public. However, other data, including key information on the status of the national reserves, are not made publicly available, and there is no freedom of information law giving citizens the right to obtain government records.
Freedom of Expression and Belief:
Singapore got mixed scores in this regard.
All domestic newspapers, radio stations, and television channels are owned by companies linked to the government. Editorials and news coverage generally support state policies, and self-censorship is common, though newspapers occasionally publish critical content. The government uses racial or religious tensions and the threat of terrorism to justify restrictions on freedom of speech. Media outlets, bloggers, and public figures have been subjected to harsh civil and criminal penalties for speech deemed to be seditious, defamatory, or injurious to religious sensitivities. Major online news sites must obtain licenses and respond to regulators’ requests to remove prohibited content. However, foreign media and a growing array of online domestic outlets—including news sites and blogs—are widely consumed and offer alternative views, frequently publishing articles that are critical of the government or supportive of independent activism.
"The Protection against Online Falsehoods and Manipulation Act" (POFMA) was adopted in May, giving government ministers the power to determine whether content is false and to order removals or corrections. The law, which was enacted despite objections from academics and civil society, had been invoked several times by year’s end, including against the political opposition.
Score Change on individuals free to express their personal views on political or other sensitive topics without fear of surveillance or retribution.
The score declined from 3 to 2 due to growing legal restrictions on free expression, including a law empowering government ministers to suppress online content that they deem false and a court ruling that allowed criminal defamation charges for criticism of the cabinet rather than a particular person.
Limited freedom of assembly:
Public assemblies are subject to extensive restrictions. Police permits are required for assemblies that occur outdoors; limited restrictions apply to indoor gatherings. Speakers’ Corner at Hong Lim Park is the designated site for open assembly, though events there can likewise be restricted if they are deemed disruptive. Non-Singaporeans are generally prohibited from participating in or attending public assemblies that are considered political or sensitive. A 2017 amendment to the Public Order Act increased the authorities’ discretion to ban public meetings and barred foreign nationals from organizing, funding, or even observing gatherings that could be used for a political purpose.
The Public Order and Safety (Special Powers) Act of 2018 granted the home affairs minister and police enhanced authority in the context of a “serious incident,” which was vaguely defined to include scenarios ranging from terrorist attacks to peaceful protests. Officials would be permitted to potentially use lethal force and to halt newsgathering and online communications in the affected area. The special powers could even be invoked in advance of a likely or threatened incident.
Activist Jolovan Wham was fined S$3,200 (US$2,300) in February 2019 for “organizing an assembly without a permit.” He had organized a conference in 2016 that featured a speech via video link by a prodemocracy leader from Hong Kong.