Counterfeit products [1] and scams [2] are persistent problems on Amazon. It's very unfair to the legitimate merchants who are trying to compete without screwing over customers. They've been yelling at Amazon for YEARS to do something about this. Presumably Amazon decided that making it harder to sign up as a third-party seller would hurt their metrics more than it would help customers.

[1] https://www.inc.com/sonya-mann/amazon-counterfeits-no-starch...

[2] https://www.inc.com/sonya-mann/amazon-fraud-scam-sellers.htm...