Drywall, drywall everywhere, yet all our walls are cracked

My husband has his own, very successful, drywall business. He works for a home manufacturer across the river in Pennsylvania. He is very good at what he does. So why does every wall in our house have cracks in it? First of all, we rent our home. Its large, and old, and contains two rambunctious boys, numerous lizards, frogs, hamsters and such. I guess it's the old adage about the shoemakers kids' going barefoot. He never has the time for our house. But there is dryed up joint compound all over the place. Anyone who's been near the stuff knows that when it dries, it crumbles easily and falls off clothing, skin, etc. I'll tell you this story real quick. One of the boys started running a fever that kept climbing to about 103 degrees. We took him to the ER, and he was diagnosed with an inner ear infection. (Which neither boy has had in his life) While the doc was examining his ear, he noticed a large, infected cut near his eardrum. Cleaning it, he found......a chunk of drywall compound. Resulting from: A wet-willy given to him by his dad when dad had some drywall under his fingernails. How did a normal person like me end up in a life like this?