A large part of the "reform minded" people are college law professors and party law enforcement committee (政法委）in Chinese. But it could as well include other people like judges, lawyers, retired party members, businessmen with connection to the government, journalists, etc. Since the revision process is not open to the public, it is not clear how they reached the decision and everyone's opinion on it. Most likely this is a long time bargaining process, where supporters of the reform argue in favor based on theoretical backgrounds and past record of abuses, while police and prosecutors claim removing it made law enforcement difficult. But this is purely speculation on my side.
It should be noted that in China basic ideas of human rights, personal dignity, respect of law, rule of law, etc are all radically different from US, even though on the surface they may look very similar. The difference stems from practice - what people used to believe right and wrong has to be redefined by law as abiding to the law or against the law in the drafting process. This means in real life often the revision of the law stems from public outcry for past malpractices, rather than a deeper appreciation of the philosophical principles behind the law or recognition of the possible benefits from the reform. Therefore it is difficult to introduce truly progressive legislation out of the blue during the revision process because public simply ignored it by large. For example, the LGBT group's rights is not really supported by the law.