Rich people who live/ed in actual mansions often end up just using a mini apartment inside the thing and the number one complaint is how long it takes to walk somewhere. They where large for parties, to support staff, and look impressive not because people actually wanted a lot of space.
Mcmansions are designed to be cheap to construct while being easy to sell. Buyers are attracted to distinctive structures as houses blend together when you look at 20+ of the things. They also default to check boxes has a pool y/n not aesthetics. Thus, your idea of 'a few good designs' makes them harder to sell.
Interestingly people with a lot of money (10-100's of millions) now days often go for small but very distinctive buildings. Think frank lloyd wright not huge but art in large part because they don't need or want lot's of staff and will often just rent out structures for party's.
Mcmansions are designed to be cheap to construct while being easy to sell. Buyers are attracted to distinctive structures as houses blend together when you look at 20+ of the things. They also default to check boxes has a pool y/n not aesthetics. Thus, your idea of 'a few good designs' makes them harder to sell.
Interestingly people with a lot of money (10-100's of millions) now days often go for small but very distinctive buildings. Think frank lloyd wright not huge but art in large part because they don't need or want lot's of staff and will often just rent out structures for party's.