Goals of doing upgrades to non-supported OSes?

We have all heard the reasons for doing these rogue upgrades, environmental, security, etc. If all we are using the machines for is to browse the internet, email, and so on, who cares if the machine is using the most current OS? Is there a higher % of unsupported apple machines being attacked due to security issues? Who knows? I'd say much of this OS churning is tinkerers and hobbyist just seeing if we can get it to work. Perhaps I see it this way because my machines are old 2010 iMac and 2012 macbook.