Thank you for taking the time to explain that. It mostly makes sense now. Back in the early 80s when I started in the business, a 26/27 inch stack was the basic standard, with maybe an intermediate cabinet plus a side cabinet. The richest mechanic I ever knew worked out of a 3-drawer Craftsman bottom box and retired at 45. He wasted no money on any tool that wasn't profitable at the time.
What we called "Taco wagons" were just appearing at that time. 40-50-something inch stacks were just really getting popular when I changed careers in 1999. So these 8 foot tall 12 foot long ginormous stacks that literally cost more than my first house still seem weird to me. I can't figure out how filling that tool condominium could possibly work out profitably for a flat-rate mechanic given the severe erosion of pay rates since I was turning wrenches. Back when the 27 inch stacks were normal, we mechanics generally got paid 50% of the labor bill. But obviously, I've been out of the business for over a quarter of a century and the pay deal must work very differently now.
I'm sure the poor, struggling, destitute shop owner could never pay 50% these days. IMO what happened was the labor rate got separated from percentages. Labor rates went up, tech pay stayed the same. Extrapolate that 50 years and there you go. You mention profitability for the mechanic - there's a shortage of qualified mechanics. Hmmm..... I have said numerous times here and in my life, the 50th percentile mechanic experience working on vehicles for the public makes zero sense. Thus, shortage. These mega boxes are the top percentages of workers, income wise.
I should do a tool box tour, it's just stupid what you need. I have a 6x6x4" case of threaded adapters to fill transmissions with. No dipstick, no fill hole, you need to pump the fluid up a stand pipe and let it equalize. Its also about having what you need to save time. I bought a 3inch horizontal extension from Snap On, like a piece of steel with a female and male lug 3" apart. Saved pulling a coolant bottle, battery, battery tray, and fuse box to deal with motor mount bolts to change trans lines. It's a balance, you'll pick some stuff that never pays back.