Couple of things going on here.

First, I think the author is completely ignoring what happens on the TV screen, given most of our most popular shows are about completely normal people.

Secondly, there has been a massive cultural shift it what it means to be "working class" these days. There aren't any coal mines anymore. We've transitioned from an industrial to an extremely 'service' based economy, so anyone who would have been working in mines, mills, or other production is now working on the till at Tesco or in a call centre.

A smaller part of this is probably also how budgets for British film were smaller back then. For 30 or 40 years we had the Carry On films being made on shoestring budgets and they were incredibly popular, which meant more of them obviously got made (movie industry largely caters to demand, they don't create it). Nowadays, especially with globalisation as well, we have huge corporations like Film 4 leading the charge in the film industry with things like The Favourite or The Father and co-producing the likes of 12 Years a Slave, 127 Hours, and Slumdog Millionaire instead. Much higher (although still incredibly small by Hollywood standards) budgets with more scope for different and interesting stories.

I think tied to that point somewhat is how Britain in general simply doesn't have the clout on the world stage that it used to. There's less attention from overseas now because we're kinda just irrelevant, or at least can't really compete against the behemoths in America.

Back on that first point though. Just to name a few successful 'working class' (to the extent it still exists) TV shows from the last two decades: Shameless, Peep Show, Inbetweeners, Outnumbered, Vicar of Dibley (ran until 2020 if you can believe it), Black Books, IT Crowd, Little Britain, Cuckoo, or even Waterloo Road. And that's obviously ignoring the fact that Coronation Street, Emmerdale, Eastenders, and Hollyoaks are all still actually running as well since god knows when.

Finally, all of this is of course ignoring the fact that films by Martin McDonagh are still getting made like Three Billboards and most recently Banshees of Inisherin.