I just wanted to share my experience that this isn't always the case. I launched a transit app in Toronto* about 3 years ago. (There were already plenty of them back then.) Over the years, daily downloads steadily grew without me doing any marketing. These days I get a few hundred downloads per day which, to me, is mind-boggling. I realize this is a bit of a special case since people now look for transit apps when they get a new phone.

* https://itunes.apple.com/ca/app/ttc-watch-for-toronto/id5052...