Calling college football a "regional sport" is inaccurate. Its a national sport, possibly America's #2 sport behind the NFL. Its more accurate to say its a national sport with a diehard rabid following in the southeast and parts of the midwest.
That said, its not surprising to see a regional matchup of a team from Alabama vs a team from South Carolina struggle a bit in ratings. Substitute one of those teams with any team from the B12, B10, or P12 and ratings increase. The ACC and SEC share too many common markets.
College Football has to figure out what it wants to do with this playoff. Semis on NYE or Dec 29 or 28 in the coming years is not ideal and a late-night weeknight Championship game with no all-day buildup.
With the NFL schedule, weekends are out for the Championship game.....and Monday nights are actually a good TV night because most people are in their homes instead of being out.
Ideally, I think going to an 8 team playoff with the quarters on Dec 31/Jan 1, semis in 2 weeks, then the Final the week before the Super Bowl would maximize ratings but then you take away from the college basketball regular season and it becomes a 2 semestwr semester sport for 4 teams.