It's basically just not profitable. The running costs are too high
The overheads are crazy and of course pub-going is declining. The days are long gone when it was cheaper for an older person to go to the pub and chat with people than light a fire at home, there's more entertainment available from Netflix or whatever and some urban areas have significant inward migration from countries like Pakistan and Poland which have zero pub culture.
That's one reason why the pubs that are doing OK have increased food provision as an extra income stream.
I'd not serve pub food to a Pole who'd not had British food though. There are many, many more dishes to choose from and you'd not generally see Glamorgan sausages, Lincolnshire haslet, cock-a-leekie or cullen skink, Halifax dock pudding (a delicious savoury dish and fits well to Polish tastes) or Suffolk pond pudding in many pubs.
I'd serve something like the ones mentioned above (apart from the pond pudding which is a swine to make). I did Lorne sausage once in Poland (rather like American meat loaf sliced and fried rather than baked) and it didn't go down well. Fishcakes do, since there's nothing really like them in PL and they are always nice.