Draining a cylinder actually takes about 20 minutes if it isn't full.
The PSI 18-step protocol requires a cylinder to be drained "slowly" (left up to interpretation, I know). We didn't used to give it much thought until one day a customer came in with some old valves that someone had given him that were newer than the old valves on his tanks. He wanted the old old valves replaced with the new old valves. The tank munky opened his valve full and let it scream until it stopped hissing, of course the valve was iced up. He assumed if the valve was open and no air was coming out, the cylinder must be empty. Then he unscrewed the valve. He said later it was "kind of hard to unscrew" but attributed it to the old junky valves probably gummed up with old lube. Then he got down to the last couple of threads and the valve blew off, flew straight up past his head, through the sheetrock in the ceiling, and lodged in the subfloor of the second story of the shop. The valve had iced up and ice had clogged the valve and there was several hundred PSI of pressure still in the cylinder.
The patch in the ceiling by the work bench is still visible today. If he'd been stooped over the cylinder more, the valve projectile wouldn't probably taken his face off. That's why you don't just open the valve and let 'er scream.
And you forgot the "You got a cutesy dumb tourist sticker from every dive shop you've ever been to and I'm going to have to spend 30 minutes scraping your silly stickers off" time. Of course, they never come off in one piece. The cheap nitrox bands that break off literally in one-inch square pieces are the worst.
Bruh, even the high school drop out working the McDonalds drive thru window gets $17 per hour now. According to my accounting, an employee costs me $20.03 per hour, break even point, and that's if he only misses 15 days of work per year (direct and indirect costs). That means he has to generate (on average) at least $35 per hour in revenue for me to justify keeping him.
So your half-hour cylinder inspection (at $25) actually COSTS me ten bucks from an accounting perspective. Thirteen bucks if you include the cost of two viton O-rings, a dab of Christolube, and a VIP sticker. Dive shops don't do visual inspections to get rich. They do it as a loss-leader service for their customers. If I stopped doing anything but visual inspections I'd be bankrupt the day after tomorrow. Visual inspections COST me money.