Dogs can do this for a number of reasons, but the most common is a simple explanation that we see all the time. When the owners brought their new puppy home, they heard a crate was necessary, so they have one ready to go. The first day, they hold the pup all day long, sits on the sofa with them, and naps in their lap. The first night, they put the pup in the crate, many for the first time, and the normalcy of the day is unsettling to the dog, so he begins to cry and bark. Depending on the pup’s self-confidence at this age, he may cry harder and harder. Most owners can’t take the crying, so they go get they pup and let him sleep with them. After all, it allows everyone to get some sleep. Fast forward to when the pup turns into an adolescent, and they no longer want the dog in their bed (and due to not being able to trust him), they need the dog to go back in the crate. Now the pup is older, stronger, and unfortunately, did not develop his self-confidence about being alone and in the crate. He first tries crying, but it doesn’t work like before so he starts trying to find a way out….if successful once, most dogs will do it over and over again.
Other possibilities are what we refer to as containment phobia, this is similar to claustrophobia for humans. And lastly, some dogs had a bad experience in a crate and it causes them much anxiety to be in one until we change that association. A “bad” experience for a dog might be harder for us humans to recognize, so many owners see no correlation and continue to force them in a space they are very uncomfortable.