If you have an opportunity to build a product that extends your employer's platform into a new target market, would you build it in house while employed to make it part of your employer's portfolio or would you quit your job build it outside?
Naive question in my opinion. A business is a lot more than just tech or software. It’s marketing, it’s customer lists, domain knowledge, accounting, connections, trust in the marketplace, etc. “If you build it they will come” is not a realistic outlook.