20+ years ago it was opposite, for ABC the 11 AM game was regional and the 2:30 game was national. Also, primetime games were a lot less common.
It changed somewhere around 2003/2004,
Presumably they did a lot of research to figure out what times people were more likely to tune-in. Not sure I get it but the differences can be millions of viewers and hundreds of millions of dollars so I guess they know what they're doing.
Definitely agree I enjoyed the CBS bigtime SEC broadcast at 2:30, I always looked forward to that.