Building like that on those lots is often against zoning code. About 3/4 of all residential lots in the US are zoned for single family homes only, and though this is changing, you’re correct that it’s not fast enough. I’d be happy to get less than what my parents bought, when I’m ready to buy. As empty nesters now, they’ve easily got 4 times as much house as they actually need or use, and my mom in particular refuses to move. Friends of mine bought a place at the market rock bottom back in about 2012, and with no kids themselves, they also have far too much house, but that’s what was available.