How many of each uniform do we have? For home openers against weaker opponents, do we suit up more players? Do we stick with traditional W/O/W due to a larger inventory of those uniforms?
I think they just tend to do the "basic" W/O/W for ho-hum non-conference games because they get the least attention.... both in terms of people in the stands and TV coverage.
They save the "cool" combos or other special looks (e.g. the '88 throwbacks last year) for big games that get a lot of attention.