not because they're oversaturated and not picking up new users or because they can't even find a buyer
But just like MySpace, it's overhyped and being destroyed by their own users MySpace died slowly as it went from social network to online brothel and awful user experience (Facebook was the nail in the coffin) Twitter is also dying slowly as it goes from megaphone news source to troll heaven and racial/sexist abuse platform
Remember this post in 3 years when Twitter gets bought by Justin Timberlake and "rebranded"