This is way back about a decade ago, when Valve was very Windows-centric and barely even had macOS ports of Steam running. Windows 8 was announced with an entirely new application type, APIs, and distribution model intended to support tablets. Existing applications were shoved in the Desktop penalty box, while new applications had to be fullscreen or side-by-side, like a tablet. Furthermore, Windows on ARM was announced, with the Desktop penalty box further restricted to
only Windows apps (though you could jailbreak it). If you wanted your app to work as a tablet app, you had to rewrite it for XAML and distribute it through the Microsoft Store, with similar technical restrictions to that of Apple's.
The very clear message from Microsoft was that the future of Windows was in fullscreen tablet apps and that the desktop - as well as third-party app stores - was going away. Valve would proceed to launch a Linux version of Steam a few months before Windows 8 RTM'd, their own Linux distro a year later, and consolized PC hardware another year after that. Basically, the whole company made a very clear pivot away from game development (which they still haven't fully gone back to) to ensure Steam had a lifeboat if Windows 9 were to drop the Desktop or enforce app lockouts on it.
Of course, what actually happened is that Windows 8 became the laughing stock of the entire PC industry. Microsoft was trying, like, five developer transitions at once and nobody was interested. (Not even Apple can do that, and they actually did try. Ask me about Rhapsody sometime.) So the end result is that app developers never wrote anything to the new native XAML APIs, users just used the Desktop app, and nobody had any interest in Windows on ARM tablets. That's why you don't remember the Windows Store lock-in; in Windows 10, Microsoft got rid of it.