Well, because there are open-source designs they'd be using. The GD32V microcontroller, for example, uses Nucleisys's BumbleBee, and high-performance chips from several vendors use Brother Honey Badger's Apache-licensed XuanTie C910: https://github.com/XUANTIE-RV/openc910

But see https://news.ycombinator.com/item?id=44503847

There are open source designs. Here is one:

https://github.com/riscv-boom/riscv-boom