Many English seaside resorts are all "gliiter" up front but can be very poor areas with little work, many people from outside coming in looking for work, and it can also attract drug addicts, drunks etc who want to to live there.
Many seaside towns also have an ageing population and the local council can be spending a fortune looking after these older people.
The other problem is that many people now go abroad for their holidays, and the holiday "season" in England can only last a few months (Easter till end of August). The rest of the year their income is very very low.
One other problem is that many of these seaside towns grew up in the Victorian era, and so the whole infrastructure of them (housing, shops, theatres etc) is crumbling
That is why Blackpool was deperate to get that huge Casino a few years ago, to halt its decline and to give it more "all year round" visitor numbers.