A family of Microsoft word processing software products for creating web, email, and print documents.
There's no one here in a decision-making role at Microsoft, so we can't answer "why" questions. My guess is that the updateable calendars depended on VBA macros to calculate the new dates. VBA is an inherent security risk because of it's power, and Microsoft has been trying to steer users away from it for years. But that's just a personal opinion.