Ironically I just left the startup world for a larger more established company and the code is some of the worst I’ve seen in a decade. e.g. core interface definitions without even have a sentence explaining the purpose of required functions. Think “you’re required to provide a function called “performControl()”, but to work out its responsibilities you’re going to have to reverse-engineer the codebase”. Worst of all this unprofessional crap is part of that ground-up 2nd attempt rewrite.

I think this is actually quite common in commercial code. At least, for most of the code I've seen. Which is why I laugh most of the time when people imply commercial code is better than most open source code. It's not, you just cannot see it.