It wasn't an impulsive decision. They kept the Daily Stormer's account active up until Andrew Anglin said CF kept offering him their services because they quietly agreed with him.

> Our terms of service reserve the right for us to terminate users of our network at our sole discretion. The tipping point for us making this decision was that the team behind Daily Stormer made the claim that we were secretly supporters of their ideology.

> Our team has been thorough and have had thoughtful discussions for years about what the right policy was on censoring. Like a lot of people, we’ve felt angry at these hateful people for a long time but we have followed the law and remained content neutral as a network. We could not remain neutral after these claims of secret support by Cloudflare.

https://blog.cloudflare.com/why-we-terminated-daily-stormer/