Because the powers that be are trying to create "Big Brother", not like we all dont assume this is the case already. But by getting companies to collect this data they can ask for more later (and in the US, a lot of companies will give up the data without a warrant). Creating systems takes time, if it already exists, adding more data points to harvest is trivial.

The whole "think of the children" angle is the trojan horse to get people who dont understand technology to support it, in hopes of making opposition to it a poison pill.