In the end though, this is true, and it's exactly what some/many people want. Some DMs want to be made to feel like their decisions cannot be wrong, and the rulebooks back that up. Some, especially those who game exclusively with friends, really like the idea of "gaming the DM" because everyone is buds around the table. Some just don't give a crap about the system at all and just want to hang out with people they like doing something they all find kinda fun; with fewer demands on rules knowledge and less demanding character creation and so forth, 5e fits that. So yeah, a system that basically just says "eh, figure it out" and the DM is like "Uh, I dunno....DC 15" works in those regards. After all, as people are pointing out, lots of people are playing the game.
For myself, I don't understand why buying a product that says "figure it out yourself" is a feature, but maybe I care too much about that. I assume professional game designers have more insight into how to run the game they've devised, and wish more of that insight had made its way in for some of these issues, but again, the expectation on my part may be what's wrong. It's just a more casual game in that regard. I suppose as long as the penalty for failing the arbitrary DC skill check isn't too egregious, it really doesn't matter.