The only reason Lucas didn't use a ton of CG in the classic trilogy was because -IT DIDN'T EXIST BACK THEN-.
If it had, you damned well better believe he would have used it.
And if you would take a just a few seconds to look into things, you would find that the bulk of the prequels were made the old fashioned way, with old fashioned models shot with old fashioned motion control cameras.
There was more modelwork on TPM than there was on the entire classic trilogy combined.