Why do people doing a rewrite need to have read the tests?

If you have good test coverage, and the tests are reliable, then what's the problem?

If your engineering culture is bad already and you don't have good test coverage or they're flaky or whatever then that is different. If that is the case, it is probably from smart-ass attitudes like yours asking these "clever" rhetorical questions to derail people trying to improve things that led it to be like that. Do everyone a favour and keep your mouth shut and let people fix things.