There are times they don't talk for days, besides basics. This is the case with many people. It is surprising but it is a fact that most marriages do not reach the stage of companionship. Obviously they are not left with much in common. This is not companionship.
People mature differently with varied likings and interests.
Soon people plan out their family. Raising kids is a job that requires both partners actively involved in all totality. There are other things in life that keep us involved and consumed. Could be settling down in life, career and a good home and so forth. While we are at all this we do not realize that as partners we may be growing apart.