Many answers, but a primary one is that MS are publicly traded and must continue to entice Wall Street to keep their stock stable/desirable.
One of MS’s preferred boasts is market share of their OS and, more specifically, the uptake rate of their latest OS. But no matter how many times they get their fingers burnt on their unilateral tactics they continue them because the marketing tail is wagging the technical/stability/security/customer satisfaction dog. The most recent debacle was the overnight automatic conversion from Windows 7 to Windows 10 which caused panic, anger, etc.
Old software, no matter how good or widespread its use, doesn’t put money in the bank. This is also why MS are obsessively hounding everyone to go to Office365 which is a subscription service and - again - a steady revenue stream. In fact, attempting to navigate the Office section of the MS site is a nightmare for those who have no interest in the 365 model - of course, this behavior is intentional.
MS (and others) imagine that marooning users on Obsolete Software Island will compel them to pay (again) for the newest version even if there is no benefit.
What MS usually ignores is that the user community are more knowledgeable and responsive than MS’ own tech support AND that the user community are willing and able to discuss issues related to old(er) versions.
Old software is vulnerable to exploits and is a distraction from new dev and bugbashing on the current os. I’ve 10 since it came out. Never had a problem even on a 10 year old laptop.
Thanks - I believe you're right on this - insightful.
But now that you shined light on what's happening my concern is that other companies could work to do the same. Honda would love to have the power to tell mechanics they are NOT allowed to repair cars older than 4 years - forcing citizens to buy new cars or risking their lives. Or refrigerators with chips that freeze the motors up after 3 years... forcing citizens to replace something they're happy with... I suspect there's a solution out there or other companies would be doing the same as MS.