I've actually been using a $3 windows 10 pro oem license in my diy pc for about 8 years, it has been bound to my Microsoft Live account and shows legit activated in their website. Also received free upgrade to windows 11 last year without any issue.
As far as I know, these were legally obtained first from Microsoft at bulk OEM rate for laptop companies to use but then sold without Microsoft's permission, maybe these laptop companies had a lot of overstock or they went out of business. I haven't seen Microsoft ever caring about how someone obtains a license and saying that one day the activation might get disabled just sounds like fear-mongering to me.
Even if people resorts to straight up piracy like using activators, I think it is still in Microsoft's best interest to keep people using Windows, because that gives them a platform to sell other Microsoft services. The more people use it, the more businesses. schools, hospitals will adopt a Microsoft ecosystem, where they can sell other pricier business subscriptions much easier.
That's the same thing with Android, Google basically gives away free licenses to phone makers so that people use their search, chrome, gmail, maps, they get to data mine, profit from personalized advertisements and from every play store app purchases.
If tomorrow Microsoft's OS market share drops below MacOS and Linux, I bet we will see Windows being offered as a free OS just like most Linux distros are today.