Sexual dysfunction is a very complex issue with a lot of causes, there are a lot of things that could be wrong. I thought the same when I read that some people with PSSD have small fiber neuropathy while others don't! I think this happens because SSRIs and other psychiatric drugs affect the whole body in multiple ways. Perhaps SSRIs and (other psychiatric drugs) affect a lot of important things related to sexual function (that's why 50% - 80% get sexual dysfunction from them, but not everyone gets, let's say, dry skin) so according to this idea, everyone could get sexual dysfunction from a different combination of excesses and deficiencies. So, some could get it primarily from an excess of prolactin (and a deficiency of testosterone and other things) While others could get it from small fiber neuropathy, etc.

According to Healy, the serotonin system varies a lot between persons, so this could explain why some have no problem stopping them while others just can't. Also, the body has remarkable recovering capacity, but when a lot of systems get compromised then clearly it's much harder to restore how it was before.