There are a few seaside towns that managed to hold on, such as Brighton. They're mostly in the South where the climate and sea temperature is a touch more bearable and you can feasibly go there on a day trip from London.
Arguably, what's happened to seaside towns in the UK is really just a more aggressive version of what's happened to all smaller towns in the UK. The UK economy has become more centralised, particularly in London but also in other major cities. Towns have little to offer the modern British economy, as the engines that kept their economies ticking over moved to China and India.
Basically, they are victims of globalisation, both in terms of easy travel and also free trade.
[Un]fortunately, the UK government keeps them just afloat by pumping tax money into them via welfare, pensions and healthcare spending. Which arguably prevents them from completely failing, but possibly reinventing themselves to be more useful and relevant to the modern economy.
The most severe deprivation in Blackpool is highly concentrated in a narrow strip just behind the seafront. The contrast is quite astonishing - Blackpool as a whole feels quite run down, but there are pockets that feel truly post-apocalyptic.
When industry and commerce located its bureaucracy within towns, this provided a social backbone. The small factory owners, trucking business owners, bank branch managers, who together with clerics, family doctors and teachers made up an established middle-class. The women usually didn't work, and had time to maintain the social fabric.
Most of this commercial, management, admin work now happens at regional, national or international level. Such professionals as there are are often on fairly short term rotations. If you're a young graduate, why on earth would you stick around..?
I (maybe obviously) know nothing about UK, but if there was a Blackpool-like town that's just like Blackpool, but inland, wouldn't that town be even less desirable?
Just like Detroit, there are a new breed of hipsters, priced out of middle class areas, starting to gentrify some areas again, for example see somewhere like Margate. But it's a slow process...
Hobart is the largest town on Tasmania, so presumably as well as tourism it is also a regional focus for industry and non-tourism services.
Blackpool is 25km from Preston (same size), a little further from Liverpool and Manchester, Leeds and Sheffield (all large cities). The industry and services are in the other cities.
Other than last year, I can't remember a year in the last 2 decades where going to the coast wasn't such a massive gamble.
Even I have given up and decided to spend a week in Turkey.
Whitstable, Padstow - food & drink.
Margate, St Ives, Folkestone - visual arts.
Aldeburgh - performing arts.
Burnham Market, Salcombe etc. - conspicuous displays of wealth.
Rock - underage drinking.
Brighton - partying hard.
etc.
Last time I was in London (early March, though many years ago) it was pretty bloody miserable too, but it seemed to be doing well enough despite that! If any given day being well be suitable for hanging out at the beach is a gamble that would seem like an argument for choosing to live near it, where you can easily make spontaneous trips when the weather suits. FWIW our most recent mini trip away was to a coastal town in Victoria in the middle of winter, where the weather was never going to be beach-suitable, other than for the dog (who loved it of course). And of course the die-hard surfers. But it was still a very pleasant getaway, with plenty to do and see, and several places we visited were booked out.