http://www.defstartup.org/2017/01/18/why-rethinkdb-failed.html
And our users clearly thought of us as an open-source developer tools company, because that’s what we really were. Which turned out to be very unfortunate, because the open-source developer tools market is one of the worst markets one could possibly end up in. Thousands of people used RethinkDB, often in business contexts, but most were willing to pay less for the lifetime of usage than the price of a single Starbucks coffee (which is to say, they weren’t willing to pay anything at all).
This wasn’t because the product was so good people didn’t need to pay for support, or because developers don’t control budgets, or because of failure of capitalism. The answer is basic microeconomics. Developers love building developer tools, often for free. So while there is massive demand, the supply vastly outstrips it. This drives the number of alternatives up, and the prices down to zero.