Much of license requirements are based on the fact that operating without proper knowledge can cause issues. You mentioned radio, which is a perfect example of this: emergency frequencies is one thing, but there are a lot of other frequencies that should be left alone. And learning which frequency ranges should and shouldn’t be used for certain activities is part of the process of obtaining a license.

Source: I have a GOC (unrestricted maritime radio certificate).

Real life example that I stumbled across as part of my job a few years ago.

1. Customer calls in needing help with his VHF radio.
2. It worked fine but his DSC calls were often traced to the wrong position.
3. Turns out some little dinghy had an incorrectly programmed radio: The owner had bought it, and when faced with question about MMSI, he had just input numbers that vaguely resembled a valid MMSI, and started using it.
4. Oops, this “bogus” MMSI belonged to our customer.

He was fined a lot for operating without a license. If he was licensed (He didn’t need the full GOC… just the one day course would’ve been enough for his use case) he would’ve known that he could have gotten his own MMSI for 20$ equivalent.

Other licenses are often based on covering costs, reducing popularity, or both. Hunting licenses here are issued based on how much moose and deer is in the area. This also covers the cost of building infrastructure to prevent them from running across roads where they really shouldn’t, and repairing farmers’ fences that have been “traversed” by moose.
Fishing in the river that runs through my town is also licensed in a similar manner: The amount (and price) of licenses is based on how much salmon there is.