Someone goes into politics because they want the power to run things.
Bureaucrats and agencies of the government want the power to run things for similar reasons, and it makes their jobs easier. Will the police ever say they do not want more powers to investigate crimes, or catch criminals? Will social services either? There are all kinds of things that can be better enforced with more information.
On top of all that they are part of the same cultural change that puts a lower value on individual liberties. It means politicians are a lot less inclined to refuse. There has also been a political drift to following expert advice with less scepticism, and the experts on these issues are the police, intelligence agencies, etc.
One cause close to my heart is that in the UK a number of local authorities keep hassling home educators (trying to bully them into sending their kids to school) even though their kids tend to do better than school going kids (their are studies showing better outcomes) because it seems inconceivable to them that people can do a better job than they do. I know people affected by this. A lot of them are utterly opposed to the idea that parents can make this decision at all.
So you admit they are not actually liberals and when they say they are they are incorrect.