I think you should understand this in the light of e.g. freedom fries and Trump's executive order re: "beautiful" public buildings. That is, once you're in a culture war, the dumbest things become battlegrounds.
Its also important to understand that the buildings in question were meant specifically as worker housing, so it was a collective project funded by workers' unions, each with particular ideologies. If you were part of the liberal housing co-op that advocated for flat roofs, you were gonna live in the flat-roof buildings. That is to say, you didn't express your politics by choosing your roof, rather, you chose your politics, and your available roof shapes were informed by that choice.
Its also important to understand that the buildings in question were meant specifically as worker housing, so it was a collective project funded by workers' unions, each with particular ideologies. If you were part of the liberal housing co-op that advocated for flat roofs, you were gonna live in the flat-roof buildings. That is to say, you didn't express your politics by choosing your roof, rather, you chose your politics, and your available roof shapes were informed by that choice.