not sure why it's not more popular.
I've had to have this discussion at work.
For non critical operations, WiFi/DECT/etc. is fine.
For anything critical, your average IT guy running the network that supports WiFi couldn't tell you the difference between UHF, VHF, VHS or VH1. To an IT guy, robust power is that they get a network device with redundant power supplies, and then plug them into the same power strip. To an average IT guy, they assume that they are experts on any and all technology, and won't ask for help and try to 'wing it'.
Usually shipboard operations are a bit more critical than that.
On a cruise ship, sure, housekeeping staff can absolutely use the network, and usually are running on DECT phones.
The UHF frequencies for shipboard use are mostly intended for i
ntraship communications or ship to dock, in other words, talking within the immediate area of the ship where VHF may not propagate well enough.
But, I agree, radio over WiFi, LTE or similar services often get overlooked.