I don't think I've heard that. Do you mean complaints that iOS should be more like Android and not require all software go through the App Store? I've definitely heard that complaint. (And made it, at least on general principle.)

If not all apps have to go through the Apple App Store and multiple App Stores are allowed that are controlled by third parties (ie: not Apple,) what makes you think those stores would be ad-free? Simply put, I think that having multiple app sources naturally leads to ads in the App Store space.

Mind you, I hate ads and am in no way arguing in favor of them.

Nothing makes me think that. :) I just don't understand what's better about the Android App Store, unless it's ad-free. (Which would surprise me, mildly, given Google's core business!)

In my entire life, I have never heard a single human being ask for more ads to interrupt their workflow or search results.

Specifically in its lack of ads or is it generally some other features they miss?

I don't know about Google Play, but Apple's App Store has absolutely horrific search. More often than not, I am googling the app name then finding the App Store link from Google Search results

App Store search is abysmal

In case you are curious about Google Play's search, you can try it on play.google.com