I was going to post the Eagles & Steve Miller Band, because I hate them, but I do get the appeal... That "easy peaceful enjoy life man" sentiment of the Eagles & Steve Miller is precisely why many people like them. I also hate Jimmy Buffet and I'd say "How can anybody like this?!" but people like Jimmy Buffet for the same reasons... relaxing party music for your parents.
Although Fleetwood Mac is fucking awesome. Well, Stevie Nix fleetwood. Go Your Own Way and The Chain.. couple awesome songs. The album Rumors is a seriously timeless album... it could be made by an alt-country band today and be groundbreaking. Shearwater/Okkervil River reminds me a lot of Fleetwood Mac.. And the Decemberists had some classic Fleetwood Mac melodies on their last album.
I would hope you like Fleetwood Mac, considering your avatar picture! Just to be clear, I love Stevie Nicks and also enjoy a lot of the material before the 1975 self-titled album. It's the other part of their catalog that sucks.
As for people liking these bands because they're simple, yeah, I get it too, but I think you can be simple without talking down to your audience. Around the same time as these three bands you also had groups like America that were very minimalistic, but at least tried to do something interesting harmonically and thematically (Ventura Highway). A great band like The Police or Steely Dan (Demolition Man/Regatta de Blanc or Show Biz Kids/Chain Lightning) can play a very simple vamp or a 12 bar blues and hold your attention for 6 minutes because they have something to say.
When I hear garbage like Big Old Jet Airliner, it feels like Steve Miller is insulting me personally. "Hey, idiot, you'll listen to anything with a beat, choke on this garbage. I'll be on my yacht". I just don't get why people like being pandered to.