A FM radio (with built-in antenna) comes in handy when there is a big blackout. …or when the phone has no coverage. …or when running out of internet data. …or on a sunny day hiking.
Besides… the physical FM/RDS chip is housed in QFN-20 packaging that measures 3×3 mm.
Oh… And I forgot to write that Traffic Message Channel (TMC) functionality would be nice too.