Having him for the stretch this year for a few million would be appealing to a number of teams. The fact that they basically had to give him away for nothing at the deadline suggests that there was significant pause by every team in taking him for next season. In the end, the Rangers had enough reason to justify grabbing him now with Cruz being suspended that they were willing to take the contract for next year.
Also, let's not act like Rios is some proven guy. He has a very inconsistent track record, and I would guess that teams accross baseball have very different opinions on his true value on the field. He's not nearly on the same level as Choo offense wise that I would be as intrigued taking a 1 year gamble on him in CF considering his 12.5M contract. I think more likely, the Reds look to extend Choo, with the hope that upon the end of Ludiwck's deal, Choo can be shifted to LF when Hamilton is ready. If that's the intial plan, I find that more preferable than forcing a square peg, in Rios, into a round hole.