They’re not done yet. Just announcing (and the verge reporting on it).
Their announcement (here) is quite forceful though, interestingly. The article described it as a manifesto.
See also a recent post here about their survey on integrating activity pub: https://lemmy.ml/post/14734757
I suspect it’s more complex than that. If they want any fediverse account to be able to subscribe, which they do, then how do they distribute content only to subscribers and not everyone on their instance?
Subscribe to the user, not the publication. If they want to actually read the article, they’ll have to log in and give them money.
This is pure speculation but it makes the most sense to me.