But there's only so many leafy greens you can grow before you saturate peoples already weak appetite.
This is the tragedy of modern commercial yield-driven market-gardening horticulture. That this is how people think salad tastes.
You can grow anything in your garden, or in a window box or whatever, and even if you've limited knowledge and don't do a pretty good job of it, it'll taste about (finger in the air) 4 to 5 times better than 85% of the stuff you buy in the shops.
What do you mean by this? The fatness epidemic hardly suggests our appetites are weak... unless you mean appetite specifically for leafy greens...