Monopolizing bus sales (or attempting to) by offering cut-rate (were they even making money?) prices for conversion to buses would make any private transit operator happy to go along. Plus, offering relatively decent (Subsidized by GM et al? Probably, but there's no proof possible at this point in time.) prices for the properties. Certainly, the trolley systems were in decline even in the early 1930's (Fresno's trolley demise was kind of a prototype for how NCL operated later), but NCL/GM/et al certainly hastened the process both directly and indirectly. And yes, they were easily able to put the smaller bus makers out of the business (though it took a while; SF for some reason didn't buy GMs until the mid-1960s by which time Flxible was the only one left, and a bit player at that). The court case was almost certainly negotiated to a minor infraction; by then there really were no alternatives to GM buses so anything serious in terms of a conclusion would have been a disaster for transit in general.

Anyway, what happened happened. We live in a different society and transportation system now, and have to deal with what is, not what might have been.