Could be related to: VoLTE support progress
So could depend on whether you have VoLTE enabled and working, and whether you have enabled CBS, and whether you have all the latest patches, and what firmware version you have on the modem.
Nevertheless, based on earlier discussions, many people would consider the lack of cell broadcasts a ‘feature’. 
(This must be a pig of a feature to test, during development, since you can’t exactly get these broadcasts on demand. Or maybe there is some way of getting a broadcast message directed to a single device?)