If it was so lucrative, wouldn’t more people set up shop undercutting the current offerings? Why not become an HVAC installer and make millions, if you’re really able to make $15k profit on a job you can turn out in a day.
The truth is probably more that the various money sinks in our society are starting to add up, things like healthcare, legal protection, licensure, compliance, rent (business or personal), even just having appropriate work vehicles, fueling them, compensating people for the time spent sitting in traffic to come across town to your house. Somehow you’re paying for all of that when someone’s livelihood is installing your mini split. A lot of those costs have grown faster than wages, if you try to point to a reason why it’s different today than 20 years ago. More people looking to make a quick buck without doing any work or providing any real value, and more people succeeding.