....how does it not?

If you are asking the question: "How does this private market solution solve the problem of government/education/medical bureaucracy being inefficient," then I guess it does not solve the root cause. But trying to solve IRB problems involving that three-headed hydra is not likely to succeed. Going around the system is a feasible workaround.

Implementing a terrible process faster at great cost is not the same thing as solving the problem, nor is it the best possible solution short of "fix all bureaucracy".

I wouldn't call my experiences in private IRB to be terrible at all, honestly.

My comment does not conflict with that because by "process" I mean the mechanism purporting to increase subject safety, not your experience.

What basis is there for the assumption that private IRBs have a "terrible process" and do a worse job at protecting subject safety?