When in doubt, follow the money
When you have a doubt why some decisions are made in life, follow the money to the real answer.
In the final half-hour of its telecast from Phoenix, ABC got a 4.6 rating. The 30-minutes it aired "America's Funniest Home Videos" got a 3.8. So ABC lost viewers. So why then would ABC switch?
Because the NASCAR race ran long, ABC had aired the commercials it had sold for the race coverage. Word is it had picked up all the money it was going to get there. By switching to its regular prime-time schedule, it also collected the money it was owed for commercials sold on that programming.