High credibility emails that deceive digitally savvy people can create a lot of warm leads who take expensive resources in phone calls and human interaction, but often fail to convert to paying victims. At some point down they funnel they realise it's a scam.
Low credibility emails generate replies from less digitally literate people who're easier to convert into a paying victim when they reply. The response rate is lower of course, but sending another email is free.
But I get your point, and eagerly await my spam with deposed princes' githubs profiles not stolen from MIT licenced projects, and blog photos not written by GPT and illustrated by DALL-E.
Perhaps what we need is a credibility coin, based on blockchain. Or a national ID card system. To prove I am who I am. As without it, I am not.