there's a ton of vegetables that grow in old climates. Basically all brassicae grow fine (cabbage, kale, cauliflower, broccoli, chard etc), and if you want to stick to roots you have carrots, beetroots, turnip, parsnip, radishes, chervil, onion, rutabaga, jerusalem artichokes etc. And beans preserve well.

I would bet the persistence of meat and potatoes is due to the higher amount of calories they provide, which historically made more sense as the productive capacity of the country was lower, and while it'd probably be ok to eat greenhouse tomatoes now, it just takes time to change habits.