Are mortality rates significantly lower in the modern developed world (I am assuming this is true) because people in general wash their hands more? Is that what you're trying to imply?

I don't buy it. I'd attribute the difference more to technologies like vaccines and antibiotics.

Proper sanitation has saved more lives than vaccines and antibiotics. Check for example this well researched Quora answer: https://www.quora.com/How-much-have-sanitation-vaccination-a...

"Proper sanitation" includes much more than just hand washing (e.g. properly disposing of urine and feces rather than throwing them into the street), so you're refuting a statement that I never made.

If you can disentangle hand washing from the effects of modern sanitation in general, I'm interested to hear more.