Texas has a warm climate, cheap housing and low taxes, which draws a lot of startups there. Raising money can be a problem, but you also don't need nearly as much - a good engineer in SV costs $250k; the same engineer in Austin costs $110k, and it's entirely possible to live on $10k a year while bootstrapping a startup. There are also a half dozen internationally-recognized engineering schools within 2 hours of I-35.
New York just has a ton of people and a ton of money. Also, the global media machine is based there as well, which is why you see a lot of media and advertising startups coming out of NYC. NYC is also attractive to people who weren't born there.