The real kicker to this is that an excerpt from the court documents for the conservatorship notes that Oher doesn’t fit the usual criteria for one, as he was already 18 and about to graduate high school at the time, and did not have any physical or mental disabilities that would normally require one.
The Tuohys (through their legal counsel) claim that they were advised by attorneys they consulted at the time to do a conservatorship in lieu of adoption, because in Tennessee it would be more complicated to adopt a legal adult. As Legal Eagle discusses near the end of the video, that’s false. It’s actually easier to adopt an adult in Tennessee than adopting a minor, because all that’s needed is the adoptee’s consent.
ETA: Supposedly the NCAA had ethical concerns about Oher going to play for Sean Tuohy’s alma mater, and the precedent that would set for wealthy people to go looking for troubled youth to groom into athletes to funnel into collegiate sports programs, and adoption/conservatorship was supposed to alleviate those concerns. That’s a matter yet to be clarified in discovery.