From business side, I don't think it has anything to do with you. Quite often it is down to luck, ability to predict where market is going next and execution.
It is tough for Monogame C# framework to compete with Unity. Your tool is basically build on top of their Monogame funnel, so if their funnel is tiny, then you screwed. But at the time it is hard to see how it was going to go, because Unity has so many problems and closed source didn't really help.
Number of problems increased exponentially on the Unity side, but it became industry standard, so today if you making games and not using Unity/Unreal and not AAA studio, it is super risky to get funded.