In the previous Banjo Kazooies, the gameplay could be endlessly extended with ever more fiendish combinations of the move set. Vehicles just can't compete with that. Once you've got an amphibious flying racecar with guns, there's just no more crazy left. Just a lot of fetch quests and time trials.
Dear Banjo, Kazooie, nuts and also bolts, here's the thing: if it was going to be love, it would have lasted until the bitter end. Oh well, gamers will always have the Jiggoseum.