In the UK, recruiters actually used to be licensed, but this requirement was largely removed in the 1970s. In researching my other article on recruiting in Japan (https://www.tokyodev.com/2020/10/01/recruiting-in-japan/), I discovered that there was a movement globally to move to ban, or at least license, private recruiting world wide as part of the Treaty of Versailles after World War I. The concern then was more that recruiters could be quite shady, to the point that it was sometimes hard to distinguish them from human traffickers.

Licensing in Japan at least is isn't about ensuring the recruiter has knowledge of the field. Rather, it is to ensure that they meet privacy requirements and are not a fly-by-night business. They include having a minimum amount of assets, have a physical office with a separate room to interview candidates, and appointing a "privacy representative" who has completed a training seminar.

Personally, I think trying to ensure that a recruiter has knowledge of a field would be quite challenging to do via licensing, especially in an area like tech where the field evolves so rapidly.