There is no doubt that wireless phone and data companies are behind the reassignment. They stand to make billions of dollars a year from the 600MHz band alone. In most markets, the loss of the 600MHz band won't make much difference for OTA TV. OTA TV stations are not that profitable any more and OTA is a shrinking market. (Cable penetration in London, ON has been 95% since the 1960s so OTA viewers here are a small part of the market.) The wireless data market, by comparison, is growing by double digits annually and is extremely profitable. Local OTA could be transmitted using a small portion of the available bandwidth. (Just take a look at the UK model to see how this works.) Distant OTA reception will take a hit but broadcasters don't care either. They want a captive local audience.
UHF station reassignment has been going on for decades. UHF originally went to channel 83. Channels 70 to 83 were reassigned before modern mobile phones became popular. (They were reassigned for cellular phone and other uses in 1983.) When the UHF band was created, the upper reaches of its frequency spectrum was considered experimental. Very few TVs had UHF tuners and UHF stations used the lower channels because TVs didn't work very well at UHF frequencies. Once the technology improved, new uses were found for higher frequencies and the attributes of UHF frequencies, for things like personal communications, became apparent.