I wonder if this has to do with the fact that people don't live their whole lives in one place as often anymore.

If I think I'm going to live out the rest of my life in my house, I'll want to change it to suit my taste, maybe even multiple times if new artistic styles crop up and I like them better.

If I'm expecting I might need to sell the house in the next five years, I'm going to prioritize having the widest possible potential buyer pool.

What puzzles me (being a casual observer) is that post-modern commercialism does not seem to affect all design domains equally. I would say that e.g. current automobile design seems to have still fairly identifiable style propositions (whether I like them being a different matter).

The forces of safety/market standards that an automobile must conform to is combining with capabilities of the materials available.

This makes the easiest/safest answers pretty standard. Automobiles combine many disciplines which makes for long development time lines. This further reduces options.

Multi-dwelling housing above 5 units will also show this same phenomenon.

Coffee makers could be very dynamic market due to fewer dependencies.