You can sell a functional prototype for a while, until customers start massively reporting bugs, someone finds a severe vulnerability, or you end up with a 1000

You can sell a functional prototype for a while, until customers start massively reporting bugs, someone finds a severe vulnerability, or you end up with a 1000 developer payroll to compensate for low maintainability and people getting checked out. Sometimes it's better to invest a bit in other aspects as well. Of course, you don't protect a $100 bike with a $1000 lock. There are tradeoffs.