To my knowledge the remainder of the bases fly for all three except MCI, which presently does AA and UA only, and IAH which does UA and DL only.

The kinds of trips each base gets just tends to shift with the seasons. There isn’t necessarily a set kind of trip per base (though some have more shorter pairings like LGA). There’s not necessarily any geographic significance. Hub bases typically have turns you can drop/trade (flica gods permitting) the first or last day of a trip to make a trip commutable, outstation bases may not.