Are they? Some may be, such as proud boys and dailystormer may be afoul of some (vague) hate speech clauses. Others may not be.
paypal and CC companies also shut down donations to wikileaks long ago (long before Trump was a thing). And even shut down donations to other foundations, such as the Wau Holland Stiftung of the Chaos Computer Club[0], that collected donations in part for wikileaks.
My first real memory of paypal was paypal shutting down the account we used to collect donations to cover server costs for a forum we ran back in the day[1], without any appeals process and freezing all assets, effectively stealing the money[2].
I also find it fascinating e.g. that cloudflare still protects botters (aka outright declared criminals) and people selling child porn[3] (aka the worst of common criminals), but dailystormer, as vile as they are, are somehow too much.
[0] German, https://netzpolitik.org/2010/wau-holland-stiftung-geht-gegen...
[1] the forums was a rather benign thing, just for chitchat, nobody sold anything, and it wasn't about anything illegal either. We never got an explanation from paypal, but the account shutdown coincided with a DMCA request for a single red carpet picture some user posted in a thread about the Emmy's. We removed that picture, by the way.
[2] Paypal wrote that they would refund the money, but some of our members reported they never did get a refund.
[3] I and some other people repeatedly reported a website selling child pornography for crypto (or for users submitting "original content"), mostly of the blackmailed-into-performing-lewd-acts variety targeting young teens and even pre-teens. While we had some success in getting domain registrars to nuke the domains in the past, this only lead to domain hopping, and finally the operator found a registrar that doesn't care (currently a Ukrainian company and .su/.pk domains). Every time the websites were behind cloudflare and every time cloudflare responded to our requests with "we're just a reverse proxy and forwarded it to the hoster" and didn't do anything. The current incarnations of those websites are still online a month later.