Milo's greatest threat was to the old school right.  Milo supported Trump and Trump is the President.  Their old guard candidates of McCain and Romney got beat handily.  The left hated Milo because he is a gay man who doesn't kowtow to leftist dogma.  Can't have any gays leaving the progressive reservation so they attacked him.  The old school right hated Milo because he helped the Republicans succeed where the old guard had failed.  Perfect storm.