They had no choice, building your own Wine takes years to decades, even for well funded companies.

The outcome is still good for the community, but it doesn't mean Valve did it out of the kindness of their hearts.

They still went all in, built a nice community around Proton itself, documented it and supported forks, etc.

Yes, because their business profited from that. It's an example in favour of GPL licenses: the interests of the public and of a for-profit venture aligned to produce value for both.

So capitalism functioned how it should, and a company wasn't a greedy douchebag. Still seems commendable to me. They had a choice. Their choice was to do what most companies do, and ignore barely-enforceable licensing; or to give back. They chose the better route.

Is Valve still just a company with profit as its main motive? Yeah, that's the point. But it can do helpful things as a side-effect.