Public dont approve of additives & fertilisers required for uniform growth of salad crops. After 80% grants 20y ago to growers, the land is now being utilised for residential homes; in my neighborhood.
Also, stocks grown cheaper in East Europe with less DEFRA interference.
Webbs Wonderfull is about the the only thing I grow these days, we start then in small pots and then plant them out in any spare spot in the borders and rockeries, get some funny comments about lettuce in the rockery but we also get some great lettuce