How do dogs understand us but can’t speak?

I know dogs voice boxes don’t physically allow them to speak human languages I also know Pavlov’s dog which is repetition, every time the dog rang the bell he would get food. But that still doesn’t answer my question. For instance my dog knows the word cage and if I tell him ‘’go cage’’ he listens and goes right in. If I say ‘’treat’’ he’s instantly excited and runs right to the treat container before I’m even there. So he obviously has comprehension of what and where things are. So he knows what I’m saying so why doesn’t he have the capability to talk to me other than being prohibited by his vocal features. Plus I know ya’ll have seen that dog on tik tok that literally starts its own conversations by pressing a multitude of sound buttons. I know this is a dumbass question but here we are.