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).