> wonder if the game would have seen more success if it was programmed using a commercially available engine, or even manually using C / C++

i don't see how a technology choice can influence commercial success tbh. It's not like there's performance issues that are fixable in C/C++, nor is there platform issues for porting (like for consoles, which is hard to a javascript stack to achieve).

The main reasons for commercial failure is due to game design, marketing and product/audience fit.