I can think of a few vital reasons:

- Browsers with add-on support, to make browsing the internet bearable

- DNS-level adblocking, to make app usage bearable

- Sideloading apps, to access software which Apple nor Google would condone

All of these are dealbreakers for me.

OS upgrades are less of a concern on Android, where apps tend to support very old versions of the OS (5.0 is not at all uncommon to be supported, which was released 9 years ago), as opposed to iOS, where it's common that only the latest two OS versions are supported. This fact alone makes it so that an Android device might even be useful for longer than an iOS-device, which is entirely locked out of basically all of the app store after 6-7 years, with no way to salvage the device any more.