I'd argue that it is not in their interests to achieve consensus, as the reward is only transaction fees, which are small compared to the stake you can confiscate from nodes who behave badly.
Thereby, as a rational actor it is in your interest to make nodes behave badly by trying to disrupt the normal consensus, and then provide the proof, draining them of their stake.
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). Perhaps even more important, the nodes have a lot of stake invested, so it's in their own interest to keep the value of the coin up in the real world. Failing to reach consensus on a consistent basis would undermine the trust in the network and make the stake useless even if they keep. Rational actors behave optimal in the long term.
You cannot drain nodes of their stake because you cannot convince the other nodes to update their ledgers accordingly.