If you go back a few years there was quite a kerfuffle here about "Employee Class" -- elites being denied upgrades or mysteriously falling off the waitlist, despite readiness to use miles / GPUs / etc., then discovering UA nonrevs and deadheaders had taken over the F cabin, possibly with help from friendly GAs. Also plenty of reports back in that era of the two or three actual customers up front getting poor / minimal service and generally being made to feel they were crashing a private employee party as cabin staff yukked it up with their nonrev friends.

No idea what the incidence of "Employee Class" shenanigans is today, but I think that is the root of the antipathy.