I'm in the industry, and there's no regulation or standardization on ccTLDs. Some of them have customized one-off web portals that an employee of the registrar

I'm in the industry, and there's no regulation or standardization on ccTLDs. Some of them have customized one-off web portals that an employee of the registrar has to log in to to manually register a domain. It's totally understandable why many registrars don't (yet?) support all ccTLDs. Contrast with gTLDs, which ICANN requires the use of standardized protocols for (see RFCs 5730-5734). Offering gTLDs is much easier; more work can be involved in signing the contracts with the registry operator than in configuring your system to point to an additional standardized API endpoint.