Source: Australian, with teenager.

1. It's not a ban on using social media, it's a requirement for age verification to create an account. This only limits usage on the few platforms that force an account to do anything.

2. The technical controls platforms implement are, unsurprisingly, generally quite weak. Kids are crafty enough to circumvent them, and share how freely.

3. Wannabe-influencer parents just create accounts for their kids, making the circumvention trivial.

4. There are no consequences for using a social media account while under 16.

I think the final point is the main one, though. By design there's no mechanism in place for the government to take any action if a kid gets onto social media, only if a platform fails to implement age checks that satisfy the legislation's criteria. So platforms all implemented tokenistic age checks. Platforms don't care, or need to care, if they get bypassed. The government doesn't care.

If I were a more suspicious man I'd say that either the point was never to reduce the use of social media by kids in the first place, or it was well intentioned but railroaded into toothlessness by lobbyists.