There were a lot of vested interests. There is nothing that makes people feel holier than though than to accuse someone of antisemitism. Basically Israel has a powerful lobby group, and the media used it to further smear Corbyn.

It was a multiple prong attack. Most people cannot and do not think for themselves. They kowtow to the loudest voice.

That said, Corbyn was weak in his leadership. Unfortunately, he wanted Brexit.