I agree with deepskyal for one of the reasons , when we dropped a coin we looked for it till it was found. And yes I am sure that there where some that we did not know about, but our Parents and Grand Parents went through the Depression were they looked for penny's under the porch to be able to mail a letter , and yes it was that bad ! And my Grand Parents where Doctors , although in a very rule area ! As it was said, no one had any money .
And this carried over to the later years were we were taught not to leave money we dropped . We did not waist even thought the real bad times were over . Most here at this site are not old enough to remember these days or the people who lived through them. And please this is not to say that anyone here is doing something wrong ! I get PM's by angry people who said I am insulting them lol .
Also like was said the older coins are most likely deep in the ground , I spent last weekend Detecting an old church that was heavily used from the 1840's . And everything we found was deep , as in 10 or more inches ! The only things we found up above that line was a few clad coins and iron junk that was tossed by builders who did the remodels .
So you not finding coins yet should not be taken as abnormal , and there are a few sites that I have done that we did not start finding anything in till we had gone back a few time. Why this happens I do not know . Because we use the same machines and go over the same places .