There are good reasons for keeping quiet when dating including, gossip, unwanted opinions, Eyein Horoh, and tznius (none of the above in any special order)
It is possible in a more open environment where people date for a length of time it may become known but in circles of strict shidduch dating lasting no more than several weeks it is not the accepted form to discuss with anyone. However I fully respect those are happy for people to know their dating/shidduch status.
In the same manner I respect those who do discuss everything with everyone but repsect must be given for those who prefer otherwise.