We only display dates for entities in the API when they're top level (except for events). I can't see any real reasons not to display them all the time. We already have them as part of the basic data, and they don't make the responses a lot bigger.

Edit: I talked to bitmap and we decided to keep this for WS3 unless people show a clear interest (while still outputting it for events by fixing MBS-13683). If people do have a clear use case, let us know!