> Approximately nobody is throwing away phones because the OEM stopped providing security patches.

This becomes a practical reason more quickly than you think. If a company only provides 4 years of security updates and they only provide 2 android MV releases, you quickly become out of date. I had a BlackBerry Key2 that I bought in 2018, I had to replace it in 2024 and I was really holding onto it despite a lot of practical problems - Slack dropped support for the version of Android a year earlier, it was only when I tried to install Google Wallet and could not that I finally decided despite the hardware and software functioning fine it really wasn't practical to use a device that was stuck on such an old version of Android. (I would've tried to figure out the kernel myself if the bootloader wasn't locked.)

But that's feature updates, not security updates? If the manufacturer kept providing security patches for your old Android version, it wouldn't have helped you install Slack and Wallet.