Of course, it's everyone's own decision what they do with their free time and it is not my place to judge anyone, but you could at least give a good idea a chance, right?
Yes I used email as a proxy, and as so many others pointed out here already (and which I agree), the Fediverse is nowhere close to being as simple as e.g. Reddit to use.
I really like your earlier idea to just recommend like 3 instances, then link to a longer-form post listing out all the various factors such as "is the instance based in the USA", "are conservatives going to feel welcomed there" (no), "what about the tankie issue", etc.
But THEN, if after all that, they either choose not to read any of it, or do and then leave, I wouldn't worry about it - bc you did your due diligence, so what more could you possibly do? And if you think of something, then yeah do that, but beyond that, it really is up to them to be willing to try new things.