oregon, washington, usc, and ucla are all like minded academic schools with the rest of the big ten. so are maryland and rutgers.
the two schools that arent are possibly usc and northwestern because they are private schools. but all of the schools are flagship institutions in their states academically and mostly large state schools.
the real question is - of course - geography.
but times change. its not 1965 anymore. once you made it all about money for the schools and then for the players, it became a whole different world. in that world, large conferences make sense.