I can't get it to thrive in Kansas City, and I don't know why. Great soil, mulched, etc...but sickly plants and some have died

I've had similar experiences. Fail to thrive, weak, etc.

However, I often see vigorous stands growing near me, with little to no care. Usually the ones I see are in full sun & end up a bit scorched looking by summer's end.

I know the probable issue for mine was that it was shaded out--i have very little full sun.

My latest stand is doing better. I put it up against the south side of the house. Some partial shade, rain will drain away after saturation, and I am completely ignoring it. I think it's a time and temperature thing, like my cauliflower this year didn't make heads because it got too hot too fast. I think we are fine in our "range" but there is more to the story, ie smoother transitions, or milder summers or more consistent water.