"rebelling against the royal family might cost him his noble title"
He is literally of royal lineage (like 3rd in line for the throne, behind his own father). Blowing up that bridge would be a spectacular way of causing a war of succession really, really fast. Besides that, trampling over the rights and privileges of nobility, especially over an alliance between a ducal house and margravial house, is how you get dynasties annihilated. Also, pissing off your marquis, the guy you gave a title to that says "this guy has extra military responsibilities?" Generally considered a bad move.