I believe the original reason for referrals was related to the breakup of the Network Solutions DNS monopoly. This led to the split between TLD registries (who run the DNS servers) and registrars (who sell domain names). To enforce the split for the big TLDs .com, .net, .org, the registration database was also split so that Network Solutions could not directly know the customer who registered each domain, but only the registrar who sold it. This was known as the “thin registry” model. From the whois perspective, this meant that when you asked about example.com, the Network Solutions whois server would only provide information about the registrar; the whois client could follow the referral to get information about the actual registrant from the registrar. Basically all the other TLDs have a “thick registry” where the TLD operator has all the registration details so there’s no need for whois referrals to registrars.
As a result, a whois client needs referral support. The top level IANA whois server has good referral data, so there isn’t much to gain from trying to bypass it.
As a result, a whois client needs referral support. The top level IANA whois server has good referral data, so there isn’t much to gain from trying to bypass it.