But they are harder and/or more expensive. That being said, they certainly don't have anywhere close to the amount of investment and research so there's probably some room to close the gap.

Sorry, what’s a GaAs?

Gallium Arsenide. Semiconductor with certain nicer properties than silicon that allow it to switch faster and have a larger operating temperature at the cost being harder and more expensive to manufacture. That's a fairly big caveat, being a lot of the reason why silicon is so ubiquitous, relegating adoption of other semiconductors to more niche applications where their more optimal properties are a necessity.