I'm so used to apps like Chrome Firefox ETC... dropping support fairly quickly far as software upgrades go. At least it deemed like they did or maybe I just expected them to support it longer than they did given the PC still worked reasonably well.
I would say 10+ years for certain OS is quite a long time. Mind you, things like browsers also have to take security into account.
A browser relies on several layers of security to protect the user. An OS like XP got dumped because it didn't support newer features like TLS 1.2+ and cert repositories. While also starting to become riddled with holes due to lack of kernel and OS updates. Things like HTML5 and other modern features also aren't supported to a certain extent due to back end things being missing from OS, drivers, and hardware running these OS. This is also why they started to drop Vista and 7 eventually.
Other things like Office could be updated continuously as a standalone but Microsoft wants you to upgrade your Office version as well as your OS so they put arbitrary limits on them. Because money.
Then you have other forms of software that don't really need to be up to date on exploit protection because they either don't rely on internet connectivity or user security. These apps only require older OS because they simply won't run correctly or even install on modern OS. A good example would be productivity software like video editors, DAWs, games, etc. They only dropped support for because the app devs work on the current versions of their software rather than trying to keep old things up to date.