Utah is a state flagship school, close enough to the PAC to make sense, and it had a recent record of winning.
Cincinnati is a largish state school in a major city.
SMU is a small private institution, a long damn ways from any other PAC institution. And their record for the last, oh, 40+ years has been horrendous. I can still remember when they went to their first bowl game post death-penalty. I'd bet they average 2-3 wins since the late 80's. At least TCU was competitive when they got the nod, and they've been a good fit for the Big 12 overall even if they didn't have to face some marquee programs (Nebraska, A&M).
Think about SMU this way. They are RIGHT in the Big 12's backyard...and the Big 12 never even glanced at them. They didn't glance, look, or pretend to drop something so they could get a better look. Never even considered them, because they make no sense.
And guess what...even now nobody cares now about Cincy or Utah.