Probably because the manual management of these requests is relatively expensive.
>"CloudFlare Registrar is not designed for the masses. There are plenty of great mass-market registrars. However, if you’re an organization where losing your domains would be a front-page story, then CloudFlare Registrar is for you."
Of course, they later did introduce a mass market offering as well, but not with that set of features! :)
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1: https://blog.cloudflare.com/introducing-cloudflare-registrar...