My wife and I do lots of vacations in warmer water, which get a lot of vacation divers, i.e., divers who dive maybe once every year or three. The common theme for vacation divers I've observed are warm water divers (as in you don't really need a wetsuit, or at most a shorty), you generally don't have your own equipment, most couldn't assemble their scuba gear (correctly) without help, not much lead weight is needed since thick exposure suits are not needed, a recent dive is in the same year, visibility under 80 ft is considered disappointing, and they have limited ability to plan and execute their own dive and return safely, let along use a compass. This is a generalization, but applies to a significant portion of vacation divers. So Cal conditions are more challenging in every aspect, and in general, people don't come to dive in So Cal expecting concierge diving. Visiting divers will often rent gear from a LDS, get help with setting everything up, and if they're really worried they will hire someone from the shop to lead them around. How many vacation divers are going to fly somewhere for a week to dive in 55 degree water with 20 ft viz as their only dives of the year?!
When we dived Molokai with Lahaina Divers at the beginning of the year, the boat was filled with more advanced divers and nobody from Lahaina Divers assembled anyone's gear. I asked about this and was told they would if asked, but are rarely asked for help since the trip catered to experienced divers. They typically will assemble gear on trips oriented toward less experienced divers.
Most of the other dive operations we dive with in Maui, like Mike Severns Diving, assemble all the gear on the boat while still on a trailer, so they can get going faster and guests aren't trying to assemble gear on board while the boat is rocking, not to mention space is limited. This isn't to say they assemble it way I set things up, but they do assemble gear correctly
Diving on So Cal dive boats can be intimidating, and probably scares off the less hard core divers. I had been diving for over 10 years before I ever started diving local boats. If you're not in a class and don't have all your own gear, including tanks and weights, you might be less likely to go out on a local dive boat, so there's less demand for the local boats to cater to vacation style divers