It's because Facebook has to constantly "innovate" to raise the share price. I'm sure Craigslist makes some decent income for it's owners and can pay it's bills

It's because Facebook has to constantly "innovate" to raise the share price. I'm sure Craigslist makes some decent income for it's owners and can pay it's bills every month but it's never going to explode in growth. They don't need new investors constantly because they don't do anything new. Their whole site is basically LAMP except for Perl instead of PHP. The latest part of their tech stack is a mail server that's 10 years old.