The hard-to-solve reason is that the pup no longer has any desire to keep his sleeping area tidy.
Housebreaking is based on the pup naturally not wanting to go to the bathroom where he eats and sleeps. This innate desire to be clean is the foundation of housebreaking. Some puppies lose, or never had, this desire. They walk through, sleep in and play on their own urine and feces. Some pups from pet stores, dirty kennels, or animals crated too early and too long who were forced to dirty themselves can usually be salvaged, if you use the proper scheduling, supervision and techniques.
Diet/Water
Feed your pup a premium puppyfood so that he does not have to eat a great deal to get the nutrition he needs. Don’t add in extras. We need his diet extra consistent right now. Be extra vigilant about your feeding and watering schedules. Even minor variations in timing, quantity or kind can cause major headaches.
Confinement
First: No bedding of any kind in the crate, and nothing absorbent that he can urinate on before shoving to the rear of the crate. And NO NEWSPAPER!!
If your pup is defecating in his crate repeatedly – and his stool is normal and he’s being walked often enough – then get him OUT of the crate. Since all housebreaking is based on the instinct to keep the crate clean, we have to get that instinct built back up BEFORE we start crating again.
Set up a small, easy-to-clean room with his crate. Keep the door off or propped open. Put the crate, food bowl, water bowl toward the front and papers in the rear. Make sure the pup can't climb on to the crate and over the gate. This will be where he is for at least several weeks. This can be a MAJOR mess and a real pain but it is necessary.
If he still dirties in his crate even with the door open, then close the door. Make the clean crate his food bowl. Just toss his dry food on to the floor. Eating off the crate floor can get some puppies trying to be clean again. Only give him access during meal times.
When you are home and want to have your pup with you, walk him then keep him on lead next to you. This way you can learn his signals and get him outside in time.
After two weeks of this, start putting him in the crate with the door closed after he has just urinated and defecated, for no more than two hours, when you are home and can watch him.
Also: Consider changing crates. Many dogs are cleaner in a plastic crate with solid sides.
Supervision
You'll need to learn his signals for when he needs to go and be extremely responsive to them. Go outside with him EVERY TIME and EVERY TIME he goes outside and gets praised and a cookie, it's a step in the right direction.
Corrections
None. Any frustration you show will either do no good or make things worse. Your pup can't help it, if he could, he would. He needs your help, not your emotional upset.
Common Mistakes
The biggest mistake is not taking this seriously. People think that this is a "puppy thing" that they will outgrow. They will not. It will in all likelihood get worse without intervention and render your dog unlivable in the long run.
Further Advice
Some clever pups learn that if they urinate in the crate they earn their freedom. If you suspect this then, when a puddle happens, take the pup out calmly, tether him nearby, clean up, and then recrate as before. Once he stops getting what he wants, he should stop making a mess.
If the mistakes start happening again, go back to the papers. You cannot rush this process. You must go the speed of the puppy. The majority of dogs, dirty or not, eventually get housebroken.
Consider shaving the belly of long-haired pups. Some that don't mind slopping around when they have longer hair clean up their act in a crew cut.