The main reason Crimea would want to join Russian Federation is fear. The fear that one day their capital would be visited by yet another "friendship train" now armed with the weaponry taken from seized arsenals of Ukrainian police forces and stomp their hopes for autonomy privileges to the ground.
I understand their disbelief towards Kiev. The brigands who recently have risen to power via violence and deception now try to teach them about what is legitimate and what isn't. It's actually even hard to take seriously.