Some people actually do this, in order to prevent them from getting into fights with each other during a time that some people are especially nervous and tense. I personally think that if a chosson and kallah cannot weather an argument or two that might arise before marriage, I don’t see how they will after the fact.
Some people hold that once the engagement is set there is no further purpose to conversation, and it could lead to untzniusdig behavior. Oo-kayyyyy…. And still other hold that way the week before the wedding. More commonly, many hold that the chosson and kallah should merely LIMIT the amount of converation they have on a weekly basis, to once a week. Again, not my thing, but who am I to decide what is right for them?