Over the years I have realized a couple things, first is usually when a feedlot wants to feed your cattle not theirs, one of two things has happened, first is they are not able to secure anymore financing than they currently have on the books. Or second is with their current operation, their cost of gain, their debt carrying load, and the current marketing opportunities they can not guarantee themselves a profit.
Thats not to say you or someone else cannot make a guaranteed profit, the numbers are all easy to find, look the numbers up, make some calculations it may work for you.