The sentence “if you're not paying for the service, you're not the customer, you're the product” might be accurate, but it would make more sense to me to say that if you're not the customer, you're the worker.
Facebook and Twitter run on unpaid labor, mostly made by abuse survivors and especially teenagers. Twitter has been enshittified pretty fast so this has been the case since at least 2012. These aren't just scam, the long-running relationship between the scammer and his victims imply most components that you would find in a standard definition of abuse, including limiting their ability to conceptualize what's happening to them, for example with hard or hidden characters limits.
Edit : I've forgot to mention that, but Mastodon also optimizes for engagement, I believe that we needed that to get attention from the media and thus to gradually build migration waves. There are good reasons to use Mastodon, but there are also forms of abuse there, total institutions as would say Goffman – defined by their inmates' isolation within a differentiated society. So there's a lot of bullshit. If we want to get rid of that, we need people to use software that won't abuse them, such as https://bonfirenetworks.org.
It was a joke :)