This not quite true I think but common practice. The same in Finland (where I am calling from).

Most just sign up because you can't have a christening without being a member of the church and even in open secular societies, some like the traditions.

We got a letter the other day reminding us that we can still have our 8 month old child baptised. Yeah right, thanks... totally forgot....

There was a compulsory church tax at one point but now it is only compulsory for members. Non-members get an equal value tax that goes to something else I think. Probably to the secret police as funding to investigate the non-members ;)