In my case, I "stick" with Delta as an alternate carrier to my preferred domestic carriers (AS, VX, WN) when the routing/timing/pricing works (it's pretty easy to avoid problematic hubs like ATL and use good hubs like SLC if you are West Coast-based like me), and because I haven't had the terrible experience the OP had (6 hour tarmac delay on international flight + bad customer service)- plus they're my preferred carrier for INTL due to my liking rows 10-28 of the A333 as being among the best Y seats for a North American longhaul carrier, their miles get full EQM credit on AS, AMS is a good European hub, and AS status is a small boost on DL.

All that being said, I've known friends who've had some pretty awful experiences with airlines similar to yours, OP, and they've "fired" or "banned" them as a result. I pretty much fired US and cleaned out my HP FF account with them once US merged with HP and went into a severe tailspin in quality- dirty planes, ripping out IFE, lots of mechanical issues. That probably is the way to go- if you don't feel the love from a carrier, take your business elsewhere.