This is why so many apps and services have problems monetizing their stuff when they start out as free and/or ad supported as a means to pump the usage numbers fast for that juicy investor funding and sky high stock valuations.

Free/ad supported is essentially the "bottom" of race to the bottom when it comes to how to make money on a product or service. And it is hard to climb the ladder of convincing people to pay for something when the core product that provides most of the value has always been free. You can't exactly just paywall the core product or people will likely feel ripped off and leave. So that leaves increasingly sketchy "value added" options.