its a free market so people are always welcome to run services that allow pseudonymity (nothing is actually anonymous on the internet, everything is logged and tracked and traceable) and people are free to use them.

the most popular services (facebook/instagram, twitter) are the ones that have the most real people posting stuff under their real names.

those companies continue to allow fake users for a variety of financial reasons but the fake users are actively degrading the experience.

twitter is working on KYC now, but it is a cheap AI version that is easily exploitable, so it won't make much of a difference (as i understand it so far).