At the bottom MS says carriers are interested but they chose to stick with Just AT&T.  Legere went as far say that MS told him it was to be exclusive.  This was a MS move and not a Verizon one as to availability.

1.  MS didn't want to pay Qualcomm licensing for CDMA

2.  MS didn't want to add further spectrum and FCC costs for testing and approval

3.  MS went exclusive with AT&T so there is no point putting in something that works for CDMA carriers

4.  MS is doing this in the short term, and I expect long term (Surface branding) will be available to all carriers like the iPhone and can be activated no matter where you bought it from thanks to Block C open access.

John Legere says T-Mobile didn't turn down Microsoft's Lumia 950 and Lumia 950 XL » TmoNews

http://www.geekwire.com/2015/t-mobiles-legere-wed-carry-the-new-windows-phone-if-microsoft-would-sto...

Update: Microsoft says in a statement:

“We’re refocusing our channel strategy, narrowing it in the short-term and planning for broader operator availability long-term. While there was interest across the board from U.S. operators, currently we’ve made the decision to have AT&T carry the Lumia 950, and then sell both the Lumia 950 and Lumia 950 XL unlocked through our own channel in Microsoft stores. In Europe, Deutsche Telekom will carry the Lumia 950 and Lumia 950 XL, and we’ll have more to share about other carriers shortly.”