I think choice of airlines and loyalty to airlines are intertwined. For example, I fly mostly on AA (and its OW partners). I first chose AA because it has the best schedules to my most frequent destinations. (A fit of pique over DL's infamous L-fare bit didn't hurt.)

Having chosen them, the lock-ins of double miles, elite perks, needing miles for next year's status, and the rest keep me with them if they're at all reasonable to my destination - even if they're not optimal on a given occasion. It has to get pretty bad, in terms of schedule, routing and/or fare, before I'll fly with anyone else. (My three RTs on non-OW airlines this year were BOS-SIN on NW, $1250 vs. $3000+; BOS-IAD, no AA service; BOS-LGA, ditto, but I got AA miles from US.)

In other words, the loyalty program keeps me on AA now, but I'm with AA for reasons that had nothing to do with it. AAdvantage is not enough better than the others to have made me choose AA just to get it, or enough worse for me to avoid AA just to avoid it.