I agree with SXO on this. I also take your point Dev - they make a lot of money from Steam. But many businesses diversify their income streams to reduce exposure to risk. All eggs in 1 basket is very risky for a company. Steam sales might trickle off if they take their eye off the ball, another competitor may swoop in (Apple, Google, Microsoft - all highly experienced in software delivery). It's why they announced non-gaming software being made available on it recently - to maximise opportunity and reduce risk.
With so much experience in engine building, I would make a heavily upgraded one and license it - it's a solid stream of B2B income completely removed from Steam.