Transaction fees are not the only reward they get, there is also a certain newly created amount distributed to nodes each round (if they reach consensus).
You cannot drain nodes of their stake because you cannot convince the other nodes to update their ledgers accordingly.
Why cant I? If consensus nodes are tricked into acting badly, the network's decision will be to confiscate their stake, following the rules.
Even if you print coins as the reward for achieving consensus, the reward from stealing stake is still greater than this by necessity, because tricking them has zero cost associated with it.