The PMS isn't where the work happens
The system runs on the reception PC. Housekeeping is on the third floor, maintenance in the basement. To set a room status someone would have to walk down. So they send a message.
Check whether the PMS has a housekeeping app or at least a mobile view; most current systems do, many houses never set it up. Two tablets or work phones are cheaper than a lost room status on a Saturday.
