Why would I upgrade to an OS that pushes ads on my login screen and start menu? Some software forces me to keep a windows machine around but I'm certainly in no hurry to upgrade from 10 to 11.
Because eventually you won't have a choice. That's how Microsoft works. Newer versions of Office come with slightly different file formats so people using older version have to upgrade. There's no plugin for new format or just degradation of the document when opening. They outright refuse.
Microsoft pushed Windows7 in similar way. New version of DirectX supported only Win7 and not older versions, even though there's no reason not to from a technical point of view. But new games supported new DirectX only and if you wanted to play better shell out those bucks.
In the end, biggest enemy to any paid software is not open source competitors, it's previous versions of their own software for the very same reason you mentioned. Why would anyone upgrade if all they need is already there. Most people don't need all the features of Office apart from different fonts and sizes, perhaps occasional table.
I'm still using Windows 7 in my home computer, for gaming no less, and only recently did some games come out that don't support it and the only significant push to upgrade is the upcoming (end of year) end of Steam support for it, which is just going to make me use my Linux partition for games more.
Roughly only in the last 2 years have I started to have any inconveniences from having Windows 7 - basically the latest KiKad, for circuit design, doesn't support it, so I kept using the previous version which has very rarelly has forced me to go find component and footpads which I would otherwise have already in the latest one.
The point being that if Windows 7 only started to get incovenient to use (both for gaming and professionally) well beyond not just Windows 8 having been launched but even Windows 10 having been launched, it's reasonable to expect that Windows 10 will still be fine for use for many years.
Fortunately I don't need gaming features on that machine, I only need to boot it to use things like Odin to flash a Samsung tablet or run crappy Nintendo Switch tools from gbatemp.
It's very much a 4th or 5th string machine for me.