Different kinds of 'investment'. You're correct that if they can't turn a profit, they won't build. Same as with cars or bicycles or any other good. But that's not a long term thing - they want to sell the goods they have produced, turn their profit, and move on to the next project.

What people who buy homes are told, though, is to essentially 'buy and hold' because it's a "good investment" that will gain value over time, even if they are not building anything or adding any value to the dwelling they inhabit.

Where I live, during the recent runup in prices, the median home gained something like $100,000 of value in a year, which is significantly more than the median household income.