I give you a hard time CD, but I absolutely agree that motivation plays a factor in bowl games. I just like to stir the pot occasionally.

Sometimes teams really don't want to be there. It might be that they were close to a CFP and had a heartbreaking loss and feel like their bowl-- or bowl opponent-- is too lowly for them. It might be that there are a number of players that plan to be NFL-bound and their thoughts are elsewhere.
There are a lot of other factors, too. There are some coaches that don't do much bowl prep at all, instead using those extra practices to prepare for the next season. There are players that have spent time on the awards circuit and get out of shape. There are players that sit out for various reasons.
I've long said that aside from a couple that might determine the MNC, bowl games are meaingless exhibitions. I'd always rather win than lose, but they're a pretty terrible way to determine relative conference strength, which is what so many people attempt to do.
IMO, early regular season OOC are far more indicitive of relative conference strength, but those matchups are so few that we're tempted to use the bowls, since supposedly, they're matching up roughly equal teams from various conferences. In reality, it simply doesn't work out that way.