Why so few enterprise start ups?

Ssssshhh... please don't spread the word about this. We[1] are working very hard on an enterprise startup, and we'd rather keep all the dosh to ourselves, thank you.

[1]: http://www.fogbeam.com

They're hard to sell to. While this is a bit of a generalism, you need someone (or many people) full-time working on relationships and getting in the door with enterprises. (Not strictly true but a common experience.)

There are actually quite a few. The reason they don't attract the younger out of college startup crowd is that the unique problems the enterprise organizations face are not well known unless you work at a few of them. That's the big secret. Once you start working, it is harder to transition and leave. Sometimes you see lower level executive departures to commercialize a technology that a bigger corp will buy.