Because elections are the way that political disputes are settled peacefully. Let's not pretend that the protests against Yanukovych were just fomented by some sort of CIA magic. Yanukovych betrayed his own electoral mandate by bowing to Russian pressure and reversing himself on the Ukraine-EU agreement. Nor can you pretend that you are protecting democracy by having an ethnic minority use foreign assistance to overthrow the local government in its own military coup.
People who would conduct a coup to get their way would have no problem stealing an election to get their way.
You just want them to legitimize your coup by voting in your rigged elections.