There is often a very limited market for underperforming hardware, which is how RISC-V chips will be starting out. There is a large amount of accumulated knowledge about, and workflow to accommodate, already established ISAs.

Due to most companies being publicly traded, taking risks is much less common, since a drop in profits could see a massive portion of the company's funds get pulled, or more likely the CEO being yanked by the board. So they play it safe and choose already established architectures.