Because auto shop tools seldom leave the nice environment of the shop. They don't go out in the rain or cold, they don't lay on the ground and get mud, sand, masonry dust, drywall dust, or who knows what else splashed, kicked on them or are subjected to submersion in said items. What do they commonly get on them - grease, oil, antifreeze, and other items that actually help protect from oxidation.
Mine leave the shop, get rained on and get laid or dropped in the dirt. I use some of them for electrical work. All my Snap on tools look brand new and they are around 20 years old. I have some Craftsman wrenches that are twice that old and have no rust on them. The other day I found a part of a motorcycle tool kit. It was dirty, but not rusted and about 40 years old.
I got rain in my toolbox once and didn't notice it for a couple days. When I got back to that tool box (I have several) all the tools, including the Kleins, were rusted with the exception of the ratchet and socket kit I bought at Advance Auto.
Has anyone ever seen a SnapOn hand wrench with rust on it?
I no longer buy Klien anything. I have a pair of Channelok linesmans that cost about 12 bucks and are better than any of the Kliens I own. After about a year, cutting wire with Klien linesmans is almost impossible. Not so with the Channeloks.
I use cheap 5-1 screwdrivers. They don't grow legs like the Kliens do and you can afford to have several sets. The bit quality is lacking, but still good for many, many uses.
I spent many years as an ASE auto tech wrenching on cars before I came into the trade. The first thing I noticed was how crappy electrician's tools were, even the ever so popular Kliens.