Cheaper than parachutes and more likely to work?
Sorry, that just popped into my head and I couldn't stop my fingers.
However in all seriousness that is a good question. I am racking my brain and I really do not remember when escape slides were first introduced. For some reason the Boeing 747 design period comes to mind. I do not recall any prop driven (piston) airliners having slides. They probably should have because the Lockheed Constellation passenger doors are higher off the ground than most any jetliner.
Someone here in pprune should know the answer.