I'm trying to think of any event I have experienced in recent memory where such a warning might have been useful.
I think this is the reason why we never set it up years ago when the standard became available.
I recall $some_random_on_the_internet admonishing me for not including tornado warning capability in the deaf alarm clock I was building. (Try explaining to USAnians that tornado warnings simply aren't a thing here; they think harry potter drinks Eggnog.) But the point is illustrative. Places prone to natural disasters tend to already have warning infrastructure in place, and updating/expanding the underlying technology as appropriate is accepted as entirely reasonable.
In the UK, it's basically severe flooding in places that are far enough from That London that politicians don't really care about them (although we're going to get more of that sort of thing in future), and once-in-a-lifetime fires or terrorist incidents. I still think it's reasonable to have it, because there's always the unforeseen and television isn't what it used to be, radio isn't accessible, and the bits of the internet that people actually use are at the whims of Californian techbros.
But the answer to the obvious 'Why now?' question appears to be "Rishi Sunak's father-in-law"...
