God imbues free will into His creations, not blind obedience. I would imagine that He gave the same to His angels.
What really frosted Lucifer's tuna was that God set humankind above the angels, when they were there first. Lucifer figured they were the firstborn, so shouldn't have to play second fiddle to such a flawed creation.
Of course, that's all speculation. God's angels aren't without their flaws either, if you read between the lines.