You note in your CATO piece:

Three states that suffered extensive tree downage from Sandy — Maryland, Connecticut and Rhode Island — forbid unlicensed tree trimming, although many a property owner would probably have appreciated the legal right to hire someone from a neighboring state to clear a blocked driveway.

I would also put forth the regulations put a damper on people keeping their trees trimmed prior to the storm. Maryland saw a great deal of outrage from people after the June derecho where trees that were not trimmed interfered and toppled power lines. Many people blamed BG&E for the lack of trimming, but one has to wonder how many people would have trimmed trees if the licensing did not exist which would have resulted in more tree trimmers at a lower cost to the consumer.

Instead, people were left with artificially high costs of tree trimming which they ignored until the untrimmed tree came toppling down on the power lines.