If you think about our most notorious pub chain - 'spoons - they generally have a decent selection of cask, so I'm not that surprised that it makes up a decent amount.
The reasons to boycott Spoons have been piling up for years. The strongarming of breweries, the use of the pubs as a pro-Brexit platform... and the bloke in charge is a notorious bellend.
Wetherspoons is cheap, but it's not a net good. (Truth be told I stopped eating there after being served a frozen curry - literally solid ice.)