Originally Posted by Efrem

If you "seldom qualify for 100% bonuses" on those airlines, you average at most 40,000 or so miles per year. At that rate it would take a quarter-century to qualify on UA if, as also posited, "you get almost all your miles from flying." Granted, that's less than the 40 years it would take on AA (with the 25% first-tier mileage bonus counting toward the higher figure of 2MM there), but to most people those are both far longer planning horizons than they want to work with.