Because they're widely being exposed for the violent communist revolutionaries that they are? Very hard to stand and defend that. That is, unless you're a Maxine Waters type hardcore lefty. She even defended the '92 Rodney King riots, where 58 people were murdered with a billion-plus in property damage due to arson and looting. They even shot at the firemen for responding. That action, btw, was instigated by an organization called the Revolutionary Communist Party. The RCP has a front operating today in the current protests called "Refuse Fascism--Drive Out the Trump-Pence Regime". In addition, the RCP is an organizer for the phony Black Lives Matter movement. See my FR Home page for much more on these groups.
By the way, the Nazi Party was a Leftist party. Need to keep driving that point home as well.