I think Spashett jumped because at the time the ShelfWeapon wasn't good enough to win for him and the new car Cyrul was working on had growing pains. He ran the Yoke because it was a killer car and proven to still be fast.
Many do jump alot until they finally get the big payday and stay. Kinwald left Reedy because Ernie could pay more of him medical bills that Reedy could. Many it is just truely a money thing. Many actually start with Schumcaher and then win a National title and bail. It is too bad but it happens just like real race drivers do. Very very few are loyal and whenever money is involved this happens as everyone wants more cash. Everyone needs cash and the more the better.