I trust Elon Musk not as far as I can throw him, but still perhaps more than one can trust Charlie Ergen.
The 12 GHz band is used for satellite downlinks. Thus the receivers have to pick up signals from thousands or hundreds of miles away. These include signals from GEOsats like, uh, Dish, and LEOsats like Starlink. The satellite TV business is apparently not as profitable as the mobile phone business, so Charlie is willing to sacrifice it in order to get free mobile spectrum, which nowadays is a financial instrument worth more in trade than in use. That is his usual business plan -- buy up licenses that are for limited, low-power use and beg the FCC to change them to higher-power, more valuable licenses. Nice work if you can get it. He's doing the same thing on the 3.5 GHz CBRS band, where they bought a bunch of Priority Access Licenses with a 47 dBm/10 MHz power limit and are asking to raise the power limit by a factor of more than 100, which of course would disrupt other users of the band.
The idea that a satellite downlink won't be interfered with by a mobile phone passing in front of it is, well, ridiculous on its face. Charlie's main excuse seems to be that Starlink is also allowed to use higher-frequency bands, which are more subject to rain fade, so they shouldn't care if 12 GHz is interfered with. Yeah, right.