You can't test quality into a product. Regardless of how much of a "QA mindset" you have, you can only ever find a fraction of defects and technical debt through external testing. This can be good enough for a throwaway app that will only be used by a limited customer base for a limited time. But that approach quickly bogs down if you try to scale it into a product that will be used indefinitely by a huge set of external customers. At some point velocity drops to near zero because the code base is such a mess that it becomes impossible to add new features without causing regression defects or breaking backward compatibility.