I ran tech support for the elderly a couple years ago. There was a ridiculous amount of people who were still on Windows 7 because they bought their laptop in 2012 and only use it to exchange emails with their grandkids, do their banking and read the news. They never bought anything new or did any major upgrades because their system doesn't "feel old" so they see no use for it.
This is also why XPs complete ESR support ended in 2019. What I just said about people also applies to certain organizations like governments, who'd rather pay through the nose for that ESR support than upgrade.
That's just the reality of it all. There's a reason why Android is so extremely pushy with installing updates to Chrome et al. in the background (and why Androids old OS depreciation process is so slow) - users just flat out don't update their software or their hardware if they don't feel the need to.
EOL from a company means nothing. People will absolutely stick on years old hardware if they can help it as long as it works for them, and you're going to still be the one on the hook unless it's truly ancient tech. (We're currently at the point where if someone uses Vista, you could probably tell them to update? Keep in mind that Vista got EOLed in 2016. Windows 7 is kinda heading in that direction, but I'm not seeing that happen until another 2 to 3 years have passed at least).
There are still more people using Firefox on Windows 7 than using Firefox on macOS (or if that's not the case anymore, the flip would have been recent).
