In some sectors software quality truly does not matter beyond a certain point (and the bar is really low). The customer very rarely has the resources or the time to try all the alternatives, especially if switching afterwards is expensive so if your marketing is good and your product works and has the needed features, you get sales, and if it's not, you don't.

Is it terrible that the app takes minutes to add a few thousand numbers? Of course it is. But it does not matter, the customer is used to software being terrible so he won't waste the time and money to switch to another software that is probably also terrible.