I mean why would you travel from Leicestershire to Southend to sit next to all those people when you could stay in the garden, the sea is not that nice, even if we were not distancing
For Storm Ellis of Leicester it was to "to take the energy from it [the sea]".
For many others it would be because sun shining = trip to the seaside and they hadn't given it any thought.
I'd expect a lot believed the beach would be really quiet as everyone else except them would be using their 'common sense'. No doubt a subset of these would have had a moan on social media about the lack of 'common sense' they witnessed.
And then of course there's the anti-establishment, anti-lockdown contrarians who want to strike a blow for the free man by finding the busiest place they can think of and sticking themselves at the heart of it. Then, when they don't die, they have their evidence!! Unless they do die, of course.
I'm not a fan of busy beaches in normal times so the prospect of visiting one right now is some way down my wish list. It's times like these I'm grateful to live in a town with no tourist appeal as I'd be curtain twitching myself to a frenzy with all these idiots turning up.