Why are there gaps between the slabs of concrete pavements?

There are 2 reasons for that.

Reason one: They can be expansion joints. In the winter the pavement contracts and in the summer it expands. these joints are generally gaps that go the whole way threw the pavement. Generally these joints are filled with some sort of caulking to keep moisture from getting underneath the pavement.

Reason two: They can be put there as joints for the concrete to crack. when sidewalks are made and other concrete pavements, they anticipate the concrete cracking, so they put in gaps that dont go all the way threw the depth of the concrete as a place for the concrete to crack and not be unsightly.