At no point could one of the entities take complete control over the blockchain by themselves and they had to agree to switch lanes together by majority vote.
That is quite the rose-colored view of the situation. From my remembrance, it was the one or two major pools on the "correct" chain that had to be persuaded to move to the forked chain to preserve the network unity. In doing so they were giving up all of the blocks they had mined, so this was not a no-nonsense decision. The decision was in the hands of a couple of people--that is not the bastion of decentralization that you make it out to be.
The power of the few to make these kinds of decisions is only temporary. Like bitcoin, pooled mining is fungible so it is very easy to switch to a different pool if the operator is making decisions that the miners do not agree with