You misunderstand what their product is at this point. Their primary product is advertising conversions by site users and visitors, with a minor secondary in user data - actual "content" is a distant third. By removing or restricting the means by which users can avoid interactions with the customer base, they drive traffic to the customer-sponsored content on the site. Yes, what they're doing will reduce organic traffic; that's the point. They would be very happy if every post visible to a user was a paid post.

Reddit is an advertising platform which allows user created content. I expect the majority of the Fediverse to go that way too within two years, regardless of Meta Threads. This is the Internet. This is what it is, what it was always going to be, and how it will be going forward.