There are millions of apps on the App Store. Unless you go viral or are featured by Apple you have little to no chance of getting any downloads.
I've had apps on the App Store since day one - literally the day the App Store went live - and I barely get any app downloads anymore.
I spend hours each day tweaking, improving, adding features, fixing bugs, and handling the new ways of doing things in each iOS release, and I still get barely any downloads.
A month ago I added Apple Ads with a high cost so they're guaranteed to be displayed, and not a single person has downloaded my apps through those ads.
I've contacted the various Mac- and iOS-related blogs and websites to see if they'll do a write-up on my apps, and they just ignore everything.
If you find the magic way of getting people to locate your apps you could probably make more money selling that info than making an app.
Too many apps, too few people willing to pay anything, and a terrible search feature in the App Store add up to no downloads. I can search for the app name of one of my apps and it will appear about 100 places down. It should be the first item listed. I'm searching for the app's exact name.
The App Store has become a flea market: lots of stalls, lots of trash.