Part of the problem is to produce a high-end RISC-V chip doesn't just need the RISC-V core. It needs all of the supporting IP as well which can be substantial

Part of the problem is to produce a high-end RISC-V chip doesn't just need the RISC-V core. It needs all of the supporting IP as well which can be substantial (interconnect, system caches, memory controllers, peripherals etc). Plus to produce something that can complete with modern mobile APs you'll need to fab on a modern process (e.g. 28 or 20nm, though that's a bit long in the tooth if you're targetting things coming out rather than matching current technology, 16FF would be better) which increases costs substantially. Simple, slow, microcontrollers can be fabbed on older and far cheaper processes.