Rob, I'm not sure? I've never seen anyone specifically plant them for foodplots as we have lots of farmers here that plant them.
Some years, there are toomany acres planted for what the plants can process and the farmers end up leaving a small percentage un harvested. (They get paid HANDSOMELY ) for doing so

If time allows, they will cultivate/ plow the ground before freeze up, if not, they will let them sit untouched this spring field work.
Those that are not dug up get little attraction compared to those that get up rooted.
When we get a hard winter (deep snow) n cold, deer will migrate for miles,(and I mean EVERY deer) to certain lands that have a beet field that was harvested. There is always a big amount of smaller beets that are left after harvesting.
As long as there is good thermal (riverbottom ) real close.
What's sad is...., when we get a real bad winter and every deer for miles will head to a certain sugarbeet field only to have it fed out by mid/ late winter and they get locked in. Snow is to deep for them to go anywhere else and MASS die offs happen. Seen it to many times.