My dad was a doctor who lost his license (nothing dramatic or gossip-worthy involved). He was primarily treating opiate addicts with something called Suboxone. It is sensitive enough that the state puts a hard limit on patients you can have - 100. This means people who need the treatment are often on waiting lists because the doctors who have the qualification to write Suboxone are often at their 100 patient limit. Father told the medical board they need to find placements for his 100 patients or they will end up dead WITH ABSOLUTE CERTAINTY. Medical board couldn't give two shits since that's not their problem, last we know at least three died within 4 months or so of not being able to find a new doctor.
All the other licensing requirements do is favor incumbents and restrict competition. Amazon was against paying local sales taxes - until they eventually figured it out; now they are a huge proponent for forcing all online retailers to have to collect all local taxes. Will squeeze out the little guys or drive them into their web store solutions.
Regulations rarely benefit small business or their customers.
Also who seriously pays attention to if someone has a license or not? You can still get a bad haircut or advice from a licensed person. What I find appalling is the more rigorous the licensing the less some people question the people who hold them. Indeed, it's now a thing to criticize any critical thinking around "experts" (such as the anointed one, Saint Fauci) - utterly disgusting.
See "Competition and Monopoly in Medical Care" by Frech.
What tends to happen, however, is that the requirements to acquire a license grow beyond basic health and safety to include a ton of formal education. This is probably due in part to the fact that practitioners are well represented among the people designing the licensing requirements, and they have a vested interest in erecting and maintaining barriers to new entrants.
For example, it typically takes 1,500 hours of instruction to become licensed to cut peoples hair in exchange for money. That amount of training might be reasonable for someone working with potentially harmful chemicals, but on the other hand I can give someone a pretty decent buzzcut and have approximately zero hours of training (but would still face civil penalties if I were to open Frankus' Buzzcut Studio).
It's also worth noting that licensing doesn't necessarily have to be enforced by the state, (although I agree that basic knowledge of the health and safety aspects of an occupation is probably a reasonable requirement to be state-enforced).
You could have a private credentialing agency that certifies practitioners who have completed additional study or exams, or have a certain minimum amount of experience (something along the lines of Microsoft's MCSE credential, but for, say, applying makeup).
I sometimes think they want to license everything because it brings in a fair amount of money in fees.
A dietitian giving bad advice could cause serious harm.
A dyslexia therapist could provide no benefit to the patient.
A cosmetologist could cause someone's hair to fall out.
Like, having something deeper than yelp reviews to help make someone's hair not fall out seems reasonable...