Full operating system with all the compatibility and device drivers. Ease of development: you program on Linux, testing on desktop Linux, and then run on a small Linux. Need additional software? Just compile and use it, without porting or adaptation/integration. I've described everything above, don't know what could I add.

ESP32-S31 is no longer an MCU anymore if it has an MMU I guess. It's a full-blown "computer chip".