The generals and any higher level officers were just important senators, many of whom have not seen much military command in the first place-again, like with Sulla.Did all those officers and men fight for Pompey because they were loyal to the Senate - or because they were loyal to their illustrious general?
Why would Pompey's son think he's in a position to declare himself dictator and March on Rome? None of his sons led an army into battle until after his death, and Sextus Pompey at least would later set himself up as an ideological defender of the traditional republican government.I suspect it was mostly the latter. And I can quite imagine a son or nephew of Pompey questioning why he and his soldiers should take orders from that bunch of greybeards in the Capitol
Because again-why would they abandon a system theyre the winners in? Pompey himself has no desire to get rid of the traditional system, his entire career is about getting to the top within that system. And of course he doesn't even control the only anti-Caesarian army.