This question originally appeared on Quora. 
Answer by Mark Rogowsky, Entrepreneur, raconteur, Forbes blogger, @maxrogo
Why didn't Twitter go public sooner?
The company is poised to make something in the vicinity of half a billion dollars this year. The threshold for a public company is somewhere around $100 million with reasonable growth.
Twitter has had solid growth for the past couple of years, ever since it successfully rolled out its in-stream advertising product. The ideal circumstance for a company to go public is to have one's ducks all lined up, performance-wise and business-wise and be in position to grow strongly in the first several years after the IPO.
For Twitter, that situation is certainly true now. Dick Costolo took over as CEO 3 years ago, stabilizing what had been a game of musical chairs. He's widely considered one of the better execs out there. Twitter's performance problems, which had plagued the service in the early days, are almost entirely a memory thanks to an extensive overhaul of what powers the site.
In the meantime, the ad products are now robust and scaling, most especially promoted tweets and ads within the stream. There is also some evidence that more elaborate ad products, using "cards" in particular, are ready to take over in the post-IPO period to help punch up growth.
This should help avoid the problems Facebook had where it hit a bit of a plateau almost as it was going public (which it has since plowed through, at least for the moment).
Great companies can go public in nearly any market conditions, as Bill Gurley and others like to say[1] and Twitter is prodigiously well capitalized, so it doesn't especially need the offering for capital. You want as many great quarters as you can get when you take your stock public. Twitter (and Facebook) squandered a bunch of very attractive ones while remaining private because there has been a bizarre backlash against being public.
The company is more than ready to be public. It has been for a while. That doesn't mean it's going to be the most successful company ever nor that it's free of issues regarding user growth and stickiness. But it's ready and its investors are doubtless pushing for even more liquidity than the private markets provides. That will help its employees too, who have a lot of vested stock, but not unlimited ability to trade it.
It's time.