Did LightSquared not know about GPS noise before bidding on the spectrum they received? Maybe LightSquared got their spectrum for cheap because there was so much noise and nobody else could find a use for it.
They purchased the spectrum to be used for satellite communications. There was an FCC loophole that allowed them to supplement satellite communications with terrestrial signals in certain cases. They decided to move ahead with a FULL terrestrial system. They decided to bet large - and lost.
Any EE could have shown the blasting a signal literally billions of times stronger in an adjacent band would completely kill functionality of devices that rightfully would never ever have expected to need to design for it.