I was the kid Ng the exact same thing - why not do like a Jaba creature or something else you can't do with a person in a costume?
One thing I did think is that if they will be outside it's got to be super hot in the costume especially in the summer and a ton of breaks would be required - animatronics don't need breaks
I agree that there's many other, arguably better uses of a full AA figure, a Jabba or any other number of things. Free-standing AA figures still seem to need support or training wheels - like the dinosaur with the cart - so it stands to reason that any full figure would be something along those lines, if they even have them. For the cost of making and maintaining an AA Wookie capable of independently walking around on 2 legs they could keep $10/hr fur characters on tap all day long indefinitely, and with better effect.