There are a lot of successful software businesses built on terrible products. In fact, in my experience, a lot of startups put far too much emphasis on software quality. As painful as it is for many developer/designer entrepreneurs to hear, if your product solves the customer's problem at a price they're happy to pay then more than good enough to sell to them, even if it's absolute garbage from a tech perspective.

There are plenty of reasons to write good quality code (it's more maintainable, moves faster, more secure, requires less resources, more fun, etc) but "because you won't be successful if you don't" really isn't one of them.