It wasn't exactly "voluntarily" -- more like "banned it after sustained public pressure", I think. They were reluctant at first but eventually caved after pressure continued to mount. The CEO wasn't happy about it.

https://en.wikipedia.org/wiki/Cloudflare#The_Daily_Stormer

(Not trying to take sides here -- it's a messy, complex topic -- just trying to recount the history as I remember it, hopefully somewhat correctly)