There is a simpler explanation - HVAC jobs are directly influenced by the push to covert everything to heat-pumps. And good heat-pumps are expensive . So when you install a $15K to $25K, installation fee also goes up. I am surprised Solar isn't up there. Panels are cheap, install is what we pay for 10 years+
Good mini splits aren't expensive. They're expensive because HVAC installers are fleecing US consumers. A majority of mini splits are made in China and are inexpensive and reliable because they're so pervasive in Asia. Most are rebadged Midea or Gree. You can get a decent mini split for <1.5K and install it yourself for $200 in tools.
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.