This is a pretty extensive TLD List, specially considering CloudFlare has to directly deal with the registries than being a reseller of some commercial registrar (like enom).
>>Ayesh+(OP)
Most of them are from Donuts, who have a huge number of TLDs. In fact, looks like the only non-Donuts domains are com, net, org, and info, so only four registries.
It's not surprising, dealing with all the various registries (especially for ccTLDs) is probably one of the harder things to scale when spinning up a new registrar. Even Amazon Route53 uses resellers for some TLDs.