Since the 1994 Ukrainian parliamentary election voter turnouts have been declining. 1994 75.81%, 1998 70.78%, 2002 69.27%, 2006 67.55%, 2007 62.03%, 2012 57.43%, 2014 51.91% and the 2019 Ukrainian parliamentary election at 49.84%. Source
This trend is not exclusive to Ukraine. Voter turnout is declining all over the world since the 1980s; although some countries do show increases in voter turnout from time to time, the general trend is downward. In Europe this trend is the most pronounced in new democracies of post-Soviet states.
There are multiple factors affecting voter turnout. Considering post-Soviet states in general and Ukraine in particular, there are several major factors.
One is perception of political problems. If a person is convinced that there is an important problem affected by the election, they are more likely to vote.
Second is perception of a single vote weight. If a person is convinced that their vote affects the outcome, they are more likely to vote.
Third is the economic development factor. Economic hardship results in voter apathy; during an economic crisis, people are more likely to focus on their basic needs and withdraw from politics.
Post-Soviet states' population was very politically active during the 1990s (voter turnout was still somewhat lower than established European democracies), but this was quickly dampened by a major economic crisis caused by the dissolution of USSR and failure of formerly communist industries to operate within a market economy environment. This crisis smoothly transitioned to global crises of 2000s an 2010s, furthering the effect. Moreover, governments formed in these states often disappointed the voters, leading to lack of faith in democratic process. Note that Ukrainian voter turnout was somewhat revitalised by the events of Orange Revolution in 2004-2005 and Euromaidan in 2013-2014.
The developments in information technologies also serve to further the loss of faith in democratic process. Information can be disseminated easely and in targeted fashion, allowing manipulation of electorate for specific goals, and finding non-partisan, proven sources is nigh impossible; moreover, social media and other internet platforms are evolving into echo chambers for specific political groups and skew perception of political landscape by users (due to local minorities being perceived as trolls and expelled). This negatively affect the first two factors discussed previously.