If you write a serious book proposal (like you’ve actually put effort into it and you have done real research) and it gets immediately turned down by an acquisitions editor, it’s very likely that the issue was fit, NOT quality
I say this so you won’t get discouraged. You shouldn’t count these responses as “rejections” IMO. Take them as a sign that you might just need to do more research on appropriate target presses, not that you need to overhaul your proposal or book
You may have even gotten the fit right but it was just that the editor recently signed a super similar book. Or they’re changing directions which you couldn’t have known about in advance
If an editor compliments your proposal but says it’s not a fit for them, take them at their word about the compliments and just move on to another editor
To clarify — move onto another editor at a *different* press, unless the first editor specifically instructs you to try one of their colleagues. A no from one editor almost always meant to represent a no from the entire press