That is false. Sylvanas called herself forsaken right at the end of frozen throne without human involvement. They showed actual hate and betrayal towards humans. Why do people repeat this thing? Forsaken are not victim of a hate campaign.
And who abandoned them? Only mostly elves(ironically their allies now) abandoned them. Plauge moved so fast in lordaeron before stormwind could do anything about it. And they could not even send help to burning steppes because of onyxia.