It's entirely Sprint's fault for not building up a reliable network (of course it's in the 2.5 GHz band) on what the FCC has given them.
Edit: Maps of the relative amount of spectrum for U.S. LTE providers is here (Sprint leads the way):
http://www.fiercewireless.com/special-reports/2015-how-much-...
Verizon has huge chucks of spectrum licenses already to work with: (https://en.wikipedia.org/wiki/Verizon_Wireless#Radio_frequen...)