Why do we make commonsense assumptions?

Consider this sentence: Jack opened the door. Whenever we are given a sentence we make commonsense assumptions about it - things that are not explicitly stated in the sentence. But why do we make them? A part of what makes a door a door is its surroundings. (Just like the meaning of a sentence resides partly in the surrounding text). A sentence tells a story. To imagine anything about a story, we need to imagine the individual elements with something in each one’s surroundings. The way the words of a sentence fuse with each other (to create meaning) contributes to these surroundings of these individual elements. The above sentence has a door. So that’s just a rectangular wooden piece which is a door. But “opening the door” makes it mandatory to imagine a frame or a wall around it since you cannot “open a door” which is just an isolated wooden rectangle standing on the ground. Hence come the other assumptions like John was wearing clothes, that he opened it with his hands, he was looking at the door while opening it etc. Another point- sometimes what happens is that we imagine a context for the sentence. This happens because once all the risings of the words have been done or the sentence has been fused fully, there is a need for a surrounding for the sentence as a whole, which manifests as the context. In other words, the earlier part refers to what can be called internal or sub-contexts whereas the latter can be referred to as external context.