alt Hacker NewsRisc-v is nowhere near dominant, people are just being swayed by headlines such as Western Digital or Nvidia shipping billions of risc-v cores.
I do find it odd that you go on and compare to x86 marketshare however, the topic you've quoted is very clearly about MCU and whilst 8086 MCU still exists they haven't been used in greenfield projects for decades. Let alone any more recent x86 implementation.
Because it's in stuff where you don't see it: in your vacuum cleaner, your toaster oven, your microwave or your electric kettle.
Do you really think Chinese manufacturers are going to buy ARM MCUs when their budget for a controller is less than 10 cents?
ARM has long ceded this market to RISC-V. It's mostly focusing on high-end application MCUs and AI now.
And lots of newer stuff is making use of standardized boards like Raspberry Pi Pico (RISC-V and ARM hybrid) or ESP32 (RISC-V too on some versions).