DirectX's various components, Direct Sound, Direct Sound 3D (Now DirectAudio), were introductions specifically for their OS in general, it's initial incarnation while a step in the right direction was buggy as hell, especially through the period in which support was provided via VXD, it matured in tandem with ALSA, but again, this is something that everyone was working towards regardless, had DirectSound not been released, ALSA would still have been introduced, as early builds were availabe much further back than the year it was finally officially included with linux distrobutions.

And even then, The goal of DirectX has almost always been squarely aimed at benefitting only the windows platform, where as OpenGL works across all platforms, and Steam can be used on Windows, Linux and Mac OS, with a large portion of the games that aren't officially supported in Linux, able to run through Wine too.

Microsofts only role has been with OS development, and by and large they have dragged their heels in doing that being slow to add new 3D features to DirectX that were long since added in OpenGL, holding back games development because developers didn't want to build games that would look better in OpenGL compared to the then-new DX6, DX7 and DX8, combine that with many miss steps and poor choices made along the way, terrible approaches to security, and with the latest versions of windows, a more narrow minded approach than ever towards supporting software outside of the windows ecosystem, Lockinmg DX12 versions of game behind the microsoft store and with Microsoft Store sold games being forced to utilize the shitty framework that causes problems for many games and in many cases also impacts performance. There have been many comparisons between Windows store sold games and Steam downloaded games running on the same system, on the same OS, and being notably better in the steam versions, a prime example being Quantum Break where the steam version not only looked slightly better, but on average hit 15-20 fps higher on the same hardware.

DirectX has it's advantages, but it is also limited to the windows platform only, something Steam is not, regardless of that, crediting PC gamings success to Microsoft is laughable at best, Microsoft have held back gaming and in some instances taken it back a few steps too, largely through a desire to restrict to their platform.

PC gamings success has little to do with them, Valves success has little to do with them too.

You should drink more often, but cool way of putting the 3 companies in gaming.

Yeah, Steam can also be used on Linux and Mac OS... for a fraction of games... years after it turned out to be a success.

And still more than 96% of the Steam hardware base uses Windows (with an upwards trend) :

Do you really believe that PC's and Valve's/Steam's success only had little to do with the groundwork Microsoft has layed out?

I think people aren't giving Microsoft enough credit.

Direct X has helped guide graphics as we know it today. It worked with all the graphics chip companies (Even mobile!) to build the API and set standards which has flowed and guided various graphics architectures that has ended up in pretty much every device we use today from Console to Mobile to High-end PC.
Game engines are also built directly for those technologies as well.

In terms of graphics technology it could be argued that no other company has been as influential overall... And thus it's partly thanks to Microsoft that Sony and Nintendo has the graphics technology that it has in their respective consoles today.

API : DirectX was only one of many used for gaming, audio API's introduced by directx only made things more streamlined, little more.
Online Infrastructure: pioneered by swoftware such as gamespy with anti-cheat systems like punkbuster.
Distribution: Again, a solution valve came up with, approached many companies including microsoft with the proposal of setting up a network of content servers, Microsoft turned them down.
PC games: Microsoft made very few games for PC, over the years, where as some 50+ per month were being released by other companies.
Compatibility: Removal of native dos in later windows systems, and prior to that, dropping 16bit microcode support essentially cut off access to the thousands of previously released games, even today a lot of games released for OS's up to Windows 7, no longer run properly on Windows 10 systems.

That "groundwork" you talk about is simply being the authors of the most commonly used OS, crediting them with the success of Steam because of that is like crediting the success of usain bolt to the guy who laid the track.

If DirectX was open source it would be a different story, but it isn't, so it's not.

Name a single Nintendo/Playstation console that uses DirectX, don't worry I'll wait.

(Tip: they, mostly, used OpenGL)

Also, what API is most commonly used in Mobile? (Ipad, Iphone, Android, etc?), ta-daaa, you got it, OpenGL ES, so a good 97+% of the smartphone marktet, compared to the WinCE/Windows phones, which last time I saw an article on it, was somewhere around 1% of the market.

But yeah, let's thank microsoft for creating a closed source API that none of the best selling games consoles or mobile platforms actually use directly or as a derivative of!..   what?

Nintendo = Innovation if you ask me

I think you are confusing API with API compatible hardware and feature sets.
You can have Direct X 12 compatible hardware without the Direct X 12 software. The hardware doesn't change because you are running a different OS or Software or API, I know it gets confusing for some people like yourself, but it's a simple enough concept once you come to terms with it.

For example, ATI introduced Tessellation on PC back in the Playstation 2 era. It wasn't untill Direct X 11 came along that it became standard industry wide on all graphics hardware. And all hardware had a Direct X 11 compatible implementation. Even mobile. Go figure? The more you know. Now you can feel a little more educated on the topic.

@OP

Maybe you could update the OP with some more explanation when you're sober.

Why thanks, without your expert knowledge, I couldn't have worked in game development on pc as far back as win95!

(yes, that's sarcasm)