Perhaps at this point, it had been long enough from the time of Eden when God spoke and interacted directly with Adam and Eve that the people of the earth no longer had the same direct nearly tangible memory of God as someone right there that they could see and hear. Maybe this means that they began praying? I wonder what "calling on" is in the original language.
Check out Strong's (OT) #7121 - to call, call out, recite, read, cry out, proclaim, ....summoned.
... a primitive root (rather identical with H7122 through the idea of accosting a person met).
You can go to many online bible sites, enter 7121, and it'll show you all the places it's used....
THank you so much for this reference!