There's a long history behind the seatbelt sign and the associated PAs that go with it to prevent the rash of pax and cabin crewmembers getting hurt. It's actually an old issue and like many other industry wide safety and procedural SOP's, cathay is behind the loop on this one as well. But better late than never. The current team is aligning and catching up in a deliberate manner, for that you can't fault them. We're literally 20 years behind the rest of the industry around here, better catch up or we'll get bitten in the @$$ and have to learn the lessons the hard way rather than learn from other people's mistakes. We're no different from any other airline out there, if they make a f'up having the same procedures as ours which failed to prevent it, we better be pro-active and fix ours as well before we have the same accident/incident. Otherwise we're very stupid for not learning from other people's mistake!
Cockpit-cabin crew communications and interaction around here is severly lacking without getting into reasons why, unfortunately. But even disregarding that fact, you can't rely on a ding to pass along important indications to the cabin. That method is pretty much outdated and used less and less today. Making a quick PA leaves no question or doubt. CRM as a whole is 20 years behind around here. What we call CRM around here, even in the cockpit alone, is not recognized as such at most other airlines. Change for the better is good. Resistance to change is human nature. If you haven't gotten used to the periodic changing of the SOP's by now or can't see the need for it, you're in the wrong business.