This is a vicious circle. For example, I started taking care of my regulator, wing and dry suit repairs myself several years ago. Reason is didn't trust any shops to do it in-house and I didn't want to be mailing them off. This in turn took business away from the shop, took away their volume and revenue, therefore shop not able to pay the technician as much.
Perhaps.
Most dive instructors do it for the love of diving, and the "free trips".
Most (real) technicians are professionals, and do it for the wages.
The problem comes in when a hobbyist dive shop owner hires a hobbyist reg tech who shows up sometimes and does a half-assed job.
I know of a number of dive shops who hire professionals who work full time servicing regs. But they aren't the norm, they tend to have government contracts to provide service, they service all equipment, not just regulators, and there are less than 10 in the country. I know 3 well enough to call the owners friend.
But you don't want to send your regs off for service, so you are self-taught (or maybe took a class), but the technology changes rapidly. Maybe you're still diving that Mark 15 ScubaPro you bought in Metarie from Dave Delgar back in 1995, nothing wrong with a Mark 15. And putting Aquaseal on a Dive-Rite 901 isn't rocket science. But I wouldn't want to jump in and repair a Mark 11 C370, I don't know a thing about them. Nor could I change the zip seal ring in my TLS-450. I personally don't want to study hard enough to learn how. Mailing gear off doesn't worry me in the slightest. I happen to be lucky enough to live near the largest navy base in the world and have a dive shop close enough that does all that stuff.
So the hobby dive shop that were ubiquitous in the late 80's through 2010 or so are failing at a fairly rapid pace. Good. Leave the dive shops to professionals who run professional shops and do things in a professional manner.