darth_ender said:

Believe me guys, I'm all about real models over CGI and I love that the new SW films will supposedly take that into account, but in this very project are AT-STs, and they happen to look very good. They also happen to be pure CGI. And while I agree that in many cases CGI doesn't quite look good enough, it seems a metal chest isn't particularly hard to create when compared to the other CGI capabilities Ady has demonstrated. Again, of course I prefer models. No need to be anti-CGI just on principle, when it is quite capable of many things. His reasons are his own, and either way, it looks pretty darn fantastic. If it's the way Adywan wanted it done, I'm cool with that. Just asking a reasonable question.

I think because the AT-ST's had to be in motion (which would necessitate motion control photography if Ady had made models), plus the fact they're fairly far away so you don't need so much realism, that's why it was more practical to go the CGI route.

Now Han in Carbonite is a completely static item, perhaps necessitating a motion track for certain shots and it's seen close up. Plus the CGI shirt would have to blend in with the real prop - easier to spot a fake in that instance I think.