Disclaimer: It's rare my day job actually intersects with HN even though I'm in the Internet industry.
Cheaper energy
Cheaper real estate
No earthquake retrofitting of datacenters
Low ping times to Midwest vs. California
Cheaper employees; less biz liability insurance required
No state income tax
Honestly, many of these are the same reasons I ended up moving to Texas after I sold my hosting company (which was based in San Jose.) I run a business here now with 15 employees and it's significantly cheaper to run it here vs. California. As a side benefit, I can also afford to own a nice house with a yard my daughter and dog can play in in a great area of Austin for about 1/5 of what it would cost in San Jose.
Why is reaching the Midwest so important?
The Chicago market (which is also very well served by Texas due to an almost direct link to DFW's Infomart, but also has a strong DC market) is the Chicago-Naperville-Elgin MSA, and is #3 on the list, and is slightly larger than Dallas and Houston's MSAs.
The three combined are 23.5 million people, and just the 3 biggest metros to note, and about a third of the people covered in the midwest. California's ping and the ping from DCs serving the Northeast (NYC MSA is #1, DC/MD/VA MSA is #6, PA/NJ-outside-of-NYC MSA is #7, Boston-Cambridge MSA is #10) is just too high for a lot of use cases.
I dunno about you, but I'm not going to tell about a third of the US population I can't serve them. There is a United States outside of California and NYC.
Edit: For completion's sake, #8 is Miami-Fort Lauderdale-West Palm Beach, #9 is Atlanta-Sandy Springs-Roswell (which both of those also are served decently by DFW, but also by DCs in VA) and the 10 largest MSAs together is about 85 million people, or about 26% of the US's population.
Because it has $3.5 trillion in GDP, and a $55,000 GDP per capita. That's larger than the economy of Germany, with a 40% higher GDP per capita. It's nearly equivalent to the combined economies of France and Russia.
There's so much space here that most companies have only recently started chasing after highly dense stuff (like 60+ drive arrays in 4U, hyper-dense blades, etc) because there just is no need to.
And as a side note, Texas now operates the largest number of wind turbines (by MW) and I think per capita as well. Texas now generates so much power that they regularly sell it to nearby states because the whole "long term storage" problem hasn't been solved at the scale Texas needs it to be...
Which means not only is datacenter space plentiful, the power is often less expensive than it is in other markets.
I'd also add that Softlayer is based in Dallas, and operates several data centers throughout the DFW area.
RagingWire is possibly the largest single company building a single campus/facility at the moment[0], and only about 2 miles from my house. It's quite impressive when you drive by and see the utterly massive power substation they built across the street too.
While the Telecom Corridor[1] name is somewhat dated, it's still growing.
[0]: http://www.ragingwire.com/wholesale/wholesale-data-center-da...
[1]: https://en.wikipedia.org/wiki/Telecom_Corridor
edit: formatting