In many places there are rules designed to make housing more expensive, such as requiring houses to be bigger than they need to be. Poor people living near you reduce the value of your house, so there's a strong incentive to make new housing less affordable.

Yes, but it takes something like 30 people working on it (honestly no idea how many are required)? so 7 months * 30 and we are getting close to 18 man years.

For a modest house you wouldn't have much more than 5 people on site at any given time.

You aren't counting the work that went into creating bricks, tiles and two-by-fours. You have to start from trees, clay and marble.

That doesn't negate the parent's point, of course.