I don't speak for BAS, but I'd say good chance both starters knew their pens were totally spent, and they needed a strong start into the 7th which would lead to the under 5 inning pick. Also, the batters are probably tired and only had a few hours sleep too. But once it got to the late innings both bullpens gave up some runs, so your Over full game cashed. Both good bets.
By the way, Overs 14-0-1 today. Road teams 12-3 I think.