It's not a slight against the engine; it's a concern about the support one can expect to receive for customizing it. Sufficiently complex games generally requir

It's not a slight against the engine; it's a concern about the support one can expect to receive for customizing it. Sufficiently complex games generally require deep cutting engine modifications, regardless of the engine used. Even Indie developers hit these hurdles from time to time, when their games explode in popularity and they find themselves porting to other platforms, adding multiplayer and social features, growing into new design elements, and so forth. I think it's a safe bet that, for instance, Innersloth and Klei have at least considered paying for such support. It doesn't matter if the engine is proprietary or not. It really doesn't. Once the cost of development of deep-cutting features in-house reaches six figures it's easy to open doors to proprietary engine developers and pay for high-quality development of those features. Generally for less than you could expect to pay if you were to pay your own developers. Well, hopefully so. ;)