The big you’ve skimmed over is that it happened under Corbyn, who was hugely popular with Labour members for being actually Left Wing, and hugely unpopular amongst the entire rest of the political and media establishments (including Labour MPs) for exactly the same reason. Pretty much everyone on all sides who’d never given a toss about antisemitism before were suddenly pearl-clutching over the tiniest statement made by a backbencher’s assistant’s brother’s gibbon because it was a handy way to bring Corbyn down without having to give any airtime to debating his (very popular) policies.