I think the answer to the question posed may just be "it's like natural selection". A lot of software is horrifically bad. But not all flaws are created equal.

I think the answer to the question posed may just be "it's like natural selection". A lot of software is horrifically bad. But not all flaws are created equal. A software that runs an online shop, but crashes 50% of the time during checkout will probably not create a successful company and thus won't survive long. However a software that has comparably many flaws and fails in all kinds of rare corner cases, but still gets the job done in most average cases, may just survive, even though it's equally bad.