They failed because they're mediocre to abysmal ideas that are implemented probably just well enough to scratch the itch of a hobbyist, before outing themselves as flops in the real world. And any that are actually good ideas with a poor interface need to be rewritten anyways, either to improve the UI or scale with growth/success. So beyond "the idea" of the app (which might have value in some cases), the majority are actually worth less than nothing, they're the proven failures. It's like shopping for a formula one racecar in a junk yard, and thinking "wow, some of these even have wheels!"

You can disagree, no point in flogging a dead horse (or app). :)