It all boils down to economics. Average is cost efficient. Standardize the raw materials. Optimize the raw material for easy storage, handling and transporting. When made this way, it is also easier to maintain, find parts (door handles, replacement faucet, switch boards etc.)
The chettinad houses are super customized. The pillars are from Burma (Myanmar) teak wood seasoned for months in sea water, the walls are polished with egg white (no paint), the tile work and the intricate carvings on the doors and pillars are all a pain when it comes to economics.
It is not just the cost to maintain them. The people with knowhow on how to maintain these are long gone. The new generation engineers only know how to build things the standard/average way with the standard materials.