There is no “talking about doing it for Reddit” here. Targeting a measure like this at specific companies is all sorts of gross, it has to be a case of what’s good for the goose is good for the gander.
There’s no reasonable definition of who should and shouldn’t be affected by this where Facebook has to comply but Reddit doesn’t.
The reasonable basis is that Facebook have consistently shown themselves to be a bad actor. I'm not arguing that age checks are a good thing, just that I don't see a reason why the law can't explicitly target companies that are detrimental to society. You might then argue Reddit should also be included for similar reasons.
I would suggest this is generally better than an attempt to codify in law some kind of definition of what companies should be covered.
There’s no reasonable definition of who should and shouldn’t be affected by this where Facebook has to comply but Reddit doesn’t.