That's because de-platforming doesn't actually fix anything. Instead of refuting the idea on its merits and allowing there to be a logical destruction of extremist views, de-platforming just turns people into "martyrs" for their cause.
I also object to the way they censor others. People act like mobs on social media. Over the years I observed lots of open source developers get mobbed because they shared some wrongthink on Twitter or whatever, or because they refused to accept some code of conduct, or even because of innocuous comments. It sucks.
This always attracts the panicky lil shits who think it's the end of the world and tell me I'm a dumb antivaxxer. There's more of them than me, so I'm an extremist now.
Apparently I'm an extremist spreading misinformation. Why else would I get downvoted?
Martyrs with very limited reach is a decent compromise.
They live among everyone else and many need help, never forget that.