In all fairness, though, while a Store listing doesn't guarantee users, the absence of a Store listing does guarantee no users. Epic found this out with Fornite when they tried to get users to sideload via their own website. So a Store listing is a necessary-but-not-sufficient condition.
The user funnel seems to be awareness via non-Store marketing channels -> search on Play/App Store -> install. Remove the second step and your funnel disintegrates.
On the other hand, it's also possible that Fortnite's Android woes were due to artificial hurdles (e.g. requiring users to first navigate menus to allow "unsafe" side-loading). I suspect they don't have this difficulty on PC where it's just a simple go to website->download->install.
I'm not sure how to account for that fairly, it seems wrong to charge for prominent listing, but on the other hand it seems wrong to charge small indie devs the same as the majors while shuffling them in deep in the catalogue. Maybe the discount for small publishers Apple announced recently will help with this, though that system does seem to have it's own flaws.
Major apps don't really need that anyways. One of the promotions on the iOS App Store is "If you love indoor plants". The first three apps in that story are "Get some inspiration: Instagram, YouTube, Pinterest". I sincerely doubt any of those three needed any additional promotion in order to get App Store downloads. The apps that actually would benefit from getting promoted, and also the Ebay app, are further down in the article.
I suspect this is a big part of it. I chickened out installing a 3rd party App Store once because Google’s warnings sort of make it sound like you’ll lose the permission prompts on individual apps. Even side loading a single app I think it might be a bit ambiguous.
No matter what the details are, side loading is always an intentionally degraded experience regardless of platform based on my experience.
I know little about the apple store but there is a lot of content on the play store with most of it bring drek and the search is terrible.