Why can't i order certain top level domains (TLDs)

Some TLDs have special requirements a registrant has to fullfill in order to be able to register a domain. Some country code TLDs require that you live in the country the TLD was created for. Others are reserved for govermental or international organizations, examples are .int or .gov.

So if you want to register a .de domain for example you need to provide a valid address in Germany. There are ways around this. Most registrar will offer a trustee service and register the domain for you. As far as the registry is concerned you are not the owner of the domain in such a case.

The requirements for the registration of domain change surprisingly often, so if you are interested in a specific domain you might want to check regularly if you can register the domain.