Is this due to a matter of constant paid advertisements online, or is it just due to a viral word of mouth?
I agree with most of the answers already posted, but the one thing I will add is: Perseverance.
When you go into a situation hoping for a user engagement rate of 80%, but only get 20%, do not give up. If you have any power users at all, this is a great sign. That means there is something of value there. Find what works for those 20% and pivot as needed. See my Core77 article about Moneythink's misunderstood stats and the power of their power users.
I also wrote an article for NTEN Change called the 1% difference. It was related to crowdsourcing, but the principles and growth strategies can be applied to any sector or app type. Your 1% difference should help you decide if an app or feature is worthwhile.
