Sure. However, Cloudflare hide and protect the "them". The information in WHOIS, in the DNS SOA record, in the network hosting the content, in the servers hosting the DNS, in the registrar's abuse contact, all say "Cloudflare". Cloudflare'll "pass along" a message for you and will happily refuse to tell you who actually owns the site.
What's more, even when you can clearly show infringement, Cloudflare doesn't take action to stop it, even though they both can and should. Not taking action when you're informed that something is illegal is facilitation. Entities that host are not liable for the content of their clients, but entities that ignore illegal activities aren't (and shouldn't be) protected.
So there's literally no other option besides suing them, even if you want to go after the party that's using Cloudflare to do the illegal thing. You literally can't unless you sue Cloudflare and get a court (that Cloudflare actually listens to) to force Cloudflare to reveal the party they're hosting and protecting.
I'm not sure how you think "you sue them, not their hosting provider" is relevant in a discussion about Cloudflare unless you really didn't know all of this.