If they didn't exist, they would exist by now.To guys who would still play pads ... pads have been around and people have incorporated it into their modus operandi.
I'm guessing that if they didn't exist chances are that you wouldn't feel compelled to invent them and you would happily do what you do in the drums.
Just tossing the thought out there.
Over the years I've seen 1001 different pads be invented, come and go, as well as numerous attempts to make a myriad of other practice devices so that drummers can practice drums without an actual drum. Including people who thought they had invented some new revolutionary pad/practice concept only to find out 3 other companies already made the same thing.