[alephnerd]

Good question!

Just about every phone (smart or feature) is running some flavor of Unix (iOS/BSD for Apple, Android/Linux for most other smartphones, and KaiOS/Linux for feature phones).

The 1998 style Nokia brick is functionally non-existent as there is no financially viable demand for a product like that anymore.

The markets that are feature phone driven (much of Africa, poorer regions of South and Southeast Asia) are also heavily WhatsApp dependent, so the mobile OS needs to be lightweight but also support modern app functionality - which lends itself to the embedded Linux use case.

Also, no matter how much you modify and QA code, inevitably some bug will arise, and will be open to exploitation.