I confess they make good waiting places (the one in South Croydon is opposite my bus stop), and the one near Farringdon station is a good place to kill some time (because the pub opposite – the Castle – is horrid, expensive, and loud). They usually have an OK beer or two. And they supply calories and refreshment after a long hike. But I can't say that I'd consider one a destination. In the end they're competing for the bottom end of market that's seems to be rushing towards its own funeral. They make a margin out of scale. And possibly some customers just get stuck to the tables.
The Brockley Barge supplied a few frothy beverages when I lived thereabouts, but that was in the days when the other alternative was the dismal Maypole, the scariest and most unpleasant pub in Christendom. These days if you trip over in Brockley you land in a deli.