Why won’t my ribs come out fall-off-the-bone tender?

Because you have the wrong set of expectations. A properly cooked rib should be tender, of course, but it should also have a little chew to it—that’s why God gave you teeth. You should be able to gnaw the meat off the bone. Fall-off-the-bone-tender ribs have been boiled or braised in the oven, and in my barbecue religion, that’s heresy.