A decent product is just entry to the game. It sounds like what made pipedrive successful is AppSumo.
AppSumo promotion definitely played a role, but if I had to pick just 1 thing behind getting to 10k customers, this wouldn't be AppSumo. Furthermore, this wouldn't be any one thing.
Context; I've been a paying PipeDrive customer for a couple years. Not sure how I originally was exposed to the product, (not appsumo), but I've stayed because the of the product.