They don't need anything as powerful as ARM (and thus avoid the licensing fees), and it's a very price-sensitive market, so a fast 8051 + accelerator hardware is enough.
No doubt some of the more expensive ones may be ARM-based, but I think the 8051-based ones far outsell them in volume.
RV32 will turn out to be the 8051 of the present. The 8051 was the Doge Dart of embedded automation. I bought a book in Vietnamese in Vietnam in 2005 on embedded development hardware and software for the 8051. If the diagrams were any indication of the quality, the writing was excellent.
I highly doubt it. As "reduced" as RISC-V is, 8051 is still tiny in comparison.
8051s are used in applications where a 4-bit MCU (yes, they do exist and are still in widespread use) is not quite enough, or they'd have chosen one of those instead.
