The CO2 produced for the manufacture of structural concrete (using ~14% cement) is estimated at 410 kg/m3 (<200kg/tonne)[0]
Bricks are around 0.5kg CO2 per kg produced (500kg/tonne). Bricks have bit lower (but similar) density than concrete, say 2000kg/m3. That makes them a lot more pollutant than concrete. Brick require a lot higher labour and transport costs as well.
[0]: https://en.wikipedia.org/wiki/Environmental_impact_of_concre...
https://www.researchgate.net/publication/285041812_Embodied_...
Well, the wikipedia link that you provided says that there is no evidence for that claim since the houses were destroyed in the burning. Two possible explanations on wikipedia for why it was done are recycling of building material and symbolic end of houses.
I doubt there's a wide-ranging conspiracy to stop people from building their own houses in the western world. I'd rather you not build a rickety ramshackle hovel next to my house. That's why we have building codes. You're certainly able to build your own house, but it can't fall over onto mine, or cause a citywide fire, or be built with poisionous elements, or ...
I recently moved from a house built in 1918 to one built in 1965, and the complexity of the construction is immediately visible. The 1918 wood struction was rough hewn compared to the stuff in my 65 house. All the walls are straight in the 65 house. The 65 house stays cooler in the summer and warmer in the winter. I don't have constant critter intrusion. That's just moving from a 100 year old house to a 60 year old house! The new construction in our area (all high quality - they knock down one of the old 1918 houses to build a new one, no idea about tract houses) takes the efficiency and performance a level up.
This is all possible through improving building codes - no one would bother with this stuff if it wasn't required.
While there is a lot to be said for building codes, I sometimes wonder if the increasing strictness applied to individual homes is a way to ensure nobody has the option to affordably build their own home with their own hands.
(Though I only wonder, I'm not sure - because I really appreciate how great modern insulation and fire/earthquake safety is)