TDL was built the way it was because that's what OLC, the paying client, wanted. They didn't want some daring refresh of the MK concept, they wanted exact copies of what was already working in America, and that's what Disney gave them. By the time OLC was ready for a second park, they got a revolutionary one-of-a-kind park with DisneySea.
It would have been nice if Disney had insisted on a unique castle for TDL, but at the time I'm not sure anyone at Disney could have envisioned two Chinese resorts and a French one as well, and the company's resources were entirely tied up in Epcot. Once HKDL's castle redo is done, TDL's will be the only castle clone.