This is the classic "what we're trying to do is bullshit on a fundamental level so we're gonna just exempt random things until it becomes a niche issue and we can just do what we want and from there we'll just close all those exceptions over time" move.
Give it 5yr and you'll have idiots in the comments talking about how the "linux loophole" was a mistake and should be closed.
Source: history
If OSes that don't verify the age of their users are a genuinely unsafe for children, why should they be allowed just because they are open source? That doesn't seem to mitigate dangers associated with age in any away I can identify.
It's kind of a hard problem and legislators are inclined picking the lowest hanging fruit. Their primary concern is to not be smeared as child predators by their political opponents at the next election, eg "jwitthuhn voted to give gambling websites, pronographers, and pedophiles easy access to YOUR children - s/he OPPOSED age verification laws on internet sleaze!! Who's jwitthuhn really working for - you, or the people who want to exploit your kids?!!"
One can point out that such electoral pitches are dishonest bullshit until one is blue in the face, but the fact is they work on a lot of voters because most of them are not smart and don't have the energy or inclination to research every issue. And it is true that there are a lot of hustlers on the internet who are willing to either passively or actively exploit kids, and the anonymity, non-locality, and technical complexity of the internet makes that relatively easy to do and hard to prosecute. Legislators offer simplistic solutions because that's what a most of the public wants, and people often make their voting decisions based on emotional factors rather than cold rationality.
You don't need mustache-twirling villains saying 'let's impose burdensome techn regulations that perpetuate oligopolies and allow me to make another trillion dollars, a few million of which I'll send your way, mwhahahaha' to get shitty legislation (which is not to say they don't exist). It will emerge naturally by default if other conditions are right.