Why would Marquette want to be in the East? They are a midwest team.
KU was the #4 seed, so they would play the top 2-3-4 seeds. Texas was the top #2, so they couldn't play UT. So UCLA was next toughest. Gonzaga and UConn are the top #3 and #4 respectively. That's all it is. It all follows those #1 seeds.
Alabama #1 overall, so south. Houston #2, they'd want South but it's taken, so Midwest. Purdue #3, they'd want midwest but it's taken so East. KU stuck with west. Then the 2-3-4 follow except avoiding in conference matchups. None of the 2-3-4 get preferences on regions.