A cynical rewrite:
a) The farmhands have been drinking the stuff for donkeys years. It's a bland McBeer which they can drink a lot of before they get pissed.
b) We've been selling it for so long because we can't be bothered to research what else is being brewed out there.
c) Financial incentives from the brewery mean it's cheap.
By sheer coincidence, we'll be up in The Dales soon, staying close by. It was on my list of possible pubs to visit! Fortunately, the nearest pub to our cottage serves beers from the Yorkshire Dales Brewery.
I think it's becoming quite hard to find a decent pint of Landlord inside Yorkshire. TBH, it's just not the same beer it was in the 80s and early 90s.
I've heard it's brewed in Hartlepool, as well.