Steam has an important reason for growing alternatives to Windows gaming: stop Microsoft from being able to extinguish non-Microsoft PC gaming.

Just imagine if DirectX 13 was XboxTM Game Store exclusive...

I paid for a CodeWeavers' CrossOver lifetime license. Their employees contribute to Wine. I don't know what software they specifically try to make sure works, but Office 2016 and Adobe CS6 works very well.

Bingo. If you need Adobe CC and want a unix-y environment then you're using it on a Mac. And there is a cost incentive for Adobe and Apple to make them work.

Valve is expanding into the linux/unix space because Microsoft has set up their MS Store, which threatens to undermine them directly.

Exactly. And to be fair, I doubt Valve is making a lot of money off of Proton on Linux. I consider it more of a philantropy project from Gabe Newell.

While I do appreciate Valve's support of Linux, it's hardly altruism: it gives them some room to negotiate with/pressure Microsoft. (i.e. while it would be painful to push even a fraction of their users over to it, it is an option Valve has) Compare that to the situation app developers on mobile platforms find themselves in these days. So it's smart strategically even if it doesn't translate into big $$$ currently.

Maybe they're not breaking bank but for a company whose revenue is measured in billions, moving the needle by .1% is worth millions..

I know many Linux users who have abandoned competitors (GOG..) for Steam due Linux support.