Welch, you gotta understand how AAA works now a days and also the actual spot the big league team is in.
AAA is a mix up of junk baller guys who can't crack an everyday MLB roster (useful for injuries when needed on the big league club but are replacement level or below, we call these guys organizational depth pieces) and a FEW top pitchers and hitters. For many years, AA has been where you see actual development, and AAA can be seen as more of "get a prospect ready by seeing failed/fringe MLB guys versus them seeing other "green" prospects" type of place.
That being said, the Nats are not contending, and there really isn't any reason to send Robles down. He isn't clogging up a roster spot and sitting on the bench. There isn't another guy pushing him off his roster spot. The best thing is to see if he can learn at the MLB level to fix his mistakes. Others have mentioned once he hits arbitration, he isn't going to break the bank, but he also will make more than I think any team is really comfortable paying him to sit in AAA. If this team was contending, sure, send him to AAA to make mechanical changes and roll with Thomas everyday. That isn't where the team is now, and Robles is going to get his chances to show he can figure it out and put all his tools together.
I know you don't like his play Welch, but this is just the way things are. Big league club can tolerate his lousy play because the other guy is probably only a bit better than him right now. Robles isn't a completely lost cause yet, so you give him time especially while the rest of the team has it's warts. I do believe he has less rope than the other young position players though, as he is about to hit arbitration and would need to show that he can break out of whatever this funk is and start producing. He looks really lost out there, and I'm fairly certain that we all are looking at a guy who is mentally struggling. I'm on the fence at this point in his development that if the FO moved him in the offseason, I wouldn't be completely flabbergasted like I would have been months ago. This FO soured on Giolito, and I could see them souring on Robles. I honestly wonder if the FO is interested in bringing up Donovan Casey to compete as well. At this point, I would say we've got three guys who could compete for CF, none of which are ideal.
Casey - Loud bat, Lots of whiffs, great arm, good speed
Thomas - Below average bat, below average power, good speed, good arm, good defense
Robles - Right now completely lost looking, but overall has the highest ceiling of them all