I never said anyone was being altruistic. The point is that right now, the ONLY thing we can do in many cases is tear down a <1500 sq ft home and build a 2400-3500 sq ft home in its place or a duplex/condo with ~2000/1000. That house being torn down is barely livable, but we can't replace it with 3-4 <1500 sq ft homes, even if there is enough land to do so. Very rarely are you seeing a house torn down that doesn't have major structural issues with it, and when you do (like one I recently demoed), while the house might be ok, due to it being built over a build line or something stupid like that, and that getting a variance is damn near impossible, there's no opportunity to do ANYTHING to the home to make it more appealing, etc.
To give you how asinine our current code is, I have a project near Shoalmont. The house is a 900 sq ft 1948 piece of crap that wasn't built particularly well in the first place. After 70 years of minimal maintenance, nearly pier is rotted out, there's severe mold and the roof is shot. The lot it is on is 11000 sq ft. It's deep, but still has about 60' of frontage. In any normal city, you could put 3-4 housing units on this, with each one in the 1500 sq ft or so range. That's three additional households not commuting down Mopac and I-35. And while they obviously wouldn't be priced at $100k each, they'd probably all fall in the $350-500k range.
Instead, we're building a 3000 sq ft home on it that will sell for $1.3M. I'm much rather build four units like I described above, but I can't because minimum lot size is 5750 sq ft, which means I can't split the lot legally into to and even if minimum lot size was not an issue (and most major cities that have minimum lot sizes are in the 3500 sq ft range), we also have minimum 50' fronts on lots (again most major cities have much smaller if they have it), and if that wasn't an issue, it's zoned SF-2, so I can't even put a duplex/condo on it, I can literally ONLY build a single family residence, and at $385k for the lot, it would be impossible to build something any smaller than about 2500 sq ft and actually make a profit.
Our existing code is specifically designed to prevent affordable housing. Don't let anyone tell you any different. It all goes back to the 1929 plan that segregated the city and pushed all the blacks to the east side.