I work for an apartment development company. To build round walls would be prohibitively expensive and impractical. Every part of your pipeline from building materials to tools to furniture is designed for linear-walled rooms.
When I was in Singapore in the early 90s, I remember my family looking at a rental unit in the Draycott towers. It was super cool looking, but lack of places for furniture to go is what nixed it.
For the curious... exterior and interior:
https://www.singaporeexpats.com/singapore-property-pictures/...
http://draycott.weebly.com/uploads/1/7/5/5/1755412/3811624.j...