It always confounds me that some long-standing college football teams have NEVER played against certain teams before.
It does seem a little unusual, especially when college football is quite professionally-maintained over the past 30 years or so, if you will. But consider a few things...
Go back further, and the seasons were shorter (10-11 game seasons), the conferences were (and most still are) based geographic divisions to make rivalries more heated, the road trips less arduous, and control costs. Go back even further (50-60) years, and there's no interstate network to easily link city to city, so the trips took some time by bus. No national, let alone regional TV broadcasts, either. Multiply that by the years and years of tradition based on mostly intra-state rivals and those in your division, and really the only way you played anyone completely out of your area of the country was in a bowl game.
Even then, the major bowls were (and mostly still are) opponents of
this-conference versus
that-conference. Most of that is to make sure fans show up for those events; I don't think many people would care if University of Miami was playing Vanderbilt in the Rose Bowl (even if they both won their conference titles), unless it was for the National Championship. But put them in a big regional bowl game, and it matters more in terms of attendance.
The other point to consider is the vast number of teams (120) in NCAA's Bowl Division; figure in the two major rivalries, the 6 or 7 conference opponents, and there's not many more games to squeeze in. The concept of a west coast team playing an east coast team (that is, if they were actually formidable opponents for one another, not some pay-to-play-in-our-house cupcake) is fairly recent, only about 15 years ago, and only very recently with some SEC teams squaring off against the Pac10/12 and Mountain West, et al.