The US used to have a steady IPO market but that has dried up in recent years. I have read that 2017 might brighten things a bit, but we'll see.
The biggest problem is SOX: going from a private company to public (something I've done twice, now) is a pain, and can take a year to implement all the regulations (you may even need to change source code, and also commit processes). It's even worse on the accounting/business side. More importantly perhaps, it's expensive: you don't want to take your company public unless you can afford the hit to productivity and cash flow.
According to the WSJ, that's why there aren't more IPOs these days.
A security nightmare, but time and time again we've seen you don't need good security to make a lot of money.