I have a hunch that we have so many simple egg-based recipes because they've gone through so much testing - perhaps in a hundred years we'll say the same thing of aquafaba.
Doesn't that say something about how eggs are easy to test compared to other things?
I think it says more about how much longer we've been using eggs, as well as how much more demand there is for alternatives today.
I was going to say that it's probably because people who had access to wheat would more likely have access to eggs, but it seems Chickpeas and Wheat were both first found around Turkey.
I just assume it is because we've had eggs longer than canned goods.
Also, even though aquafaba from freshly cooked chickpeas also works well, I'm guessing that, until recently, chickpeas weren't super common in the part of the world where the European pastry tradition developed.