> Well, Valve got seriously concerned about the Windows Store, like, a decade ago, since that could have reduced the stranglehold of Steam on the gaming marketplace

Microsoft telegraphed its intention to kill Steam. The plan was a hermetically sealed ecosystem where only cryptographically signed code could run on Windows computers, from UEFI boot to application launch. This meant users would only run software Microsoft let them, and there was no room for the Steam store in Microsoft's vision of the future then.