What you are saying here is that a writer who has spent months writing a book--probably at a substantial cost--should then bear the expense of having sensitivity readers vet his or her manuscript before submitting it to a publisher. This, in my view, is unfair to authors who aren't rich.

The expense might to hundreds of dollars if not thousands that a writer might not be able to afford at that point. It might also miss the mark when, as you say, a publisher might want to run the ms. through its own sensitivity readers. And it would be a wasted expense if the book doesn't sell unless you thought it would be helpful with self publishing:

From my perspective a fairer approach would be this: After a publisher makes a bid on a book but before the contract is signed, find out if the firm plans to submit the ms. to sensitivity readers. If so, ask that this be done BEFORE the signing and that you be allowed to see and approve any suggested changes before signing the contract. That way you would not bear the expense and could walk away from the deal if the changes are objectionable.

It's common in U.S. publishing for publishers to ask for changes before the contact is signed, so the approach I've suggested is no big departure from standard practice. And if an agent is involved, the agent could handle all the details.