#4 does... Namely legacy reasons.
I have a perfectly fine multipage scanner here that doesn't have drivers for Windows 7 and the manufacturer is out of business. You do know that Windows 7 implemented driver signing right? So even if you do find a legacy driver it probably won't start because it won't be signed. And don't give me this "Linux is your route" because no driver exists for it there either. So my choices are toss a perfectly working, expensive at the time and in demand scanner just to update from a working OS to one that doesn't or stick with what is working.... Hmmmm Hard choice that one.