I just searched for "buy coffee" in G Play and not a single one of the top 15-ish results let me buy coffee apart from one coffee shop in New York, which is off by roughly one half globe circumference. If anyone ever did that, they'd quickly realise there's nothing there and go back to a search engine.
I guess it's just that users are stupid? Like, I know calling users stupid is a bad trope and all, but this is one of those cases where the behaviour just straight up wouldn't produce usable results. Like, if they're looking to buy a bike, will they just search for "bike buying apps"? I get looking for "apps to buy things with" (like amazon, wallmart, whatever) and then picking one and seeing if they offer bikes, but looking for the product directly??
This actually seems to also contradict the recent trend of people moving to big apps like DoorDash and Amazon replacing individual apps with different niches like the McDonald's app and apps from smaller retailers. If you're looking for "buying a bike" the Amazon app won't even be on the list...
Again, all of this is my logic, I have no evidence. This is just one of those situations where something goes so strongly against my intuition that I can't imagine how it could possibly be correct. I'll have to look for some real research on this, if any is available...
I think there are a few things at play here
1. Principal agent problem https://en.wikipedia.org/wiki/Principal%E2%80%93agent_proble...
2. Illusory truth effect https://en.wikipedia.org/wiki/Illusory_truth_effect
So like you said in the beginning, it makes sense that people selling something will highlight "evidence" that it works (principal agent problem).
Marketing is counterintuitive though. Please take a look at illusory truth effect and tell me what you think.
If it is, in most cases we can just release a webview-in-an-app and render the usual responsive website on the phone. This is the low cost route to apps.
However there are products that could genuinely need an app. A Nespresso machine could be one of them: control everything from your phone and if a machine has some kind of cup automation, also make coffee from remote and walk to the machine to get the cup whan it's ready.
When it comes to these companies selling apps though, it doesn't matter what the market thinks... What matters is what the suppliers think the market thinks.