#1 His sleeping schedule changed
Let’s face it – being in a crate is kind of boring. There is not much to do for a dog inside a crate. Dogs that succeed at crate training usually do one thing in there – sleep! The puppy owners that succeed the fastest with crate training are the ones that only put their puppy in when he is tired.
As your dog ages however, his sleeping schedule will change. He will need fewer naps and less sleep overall than when he was a wee little baby.
If you put a dog that is wide-awake into a crate, chances are he is going to whine and cry. Make sure that your dog is tired and has had some exercise before he goes into the crate. You should never crate your dog after he just woke up – he has way too much excess energy at this point!
Evaluate your pup’s sleep schedule and see if you perhaps need to crate him at different times.
If you got your puppy through a rescue, it is likely that his sleep schedule will change after the first 1-3 weeks in the new home. Rescue dogs often sleep very much initially, but as they adjust to their new home their need for rest decreases.