I don't doubt that the skyline sets can be popular, but they hardly deserve the moniker of "Architecture." At best, they're a series of small monuments, and perhaps well known buildings, that inhabit a specific city. The scale is so small, it's difficult to bring out any interesting architectural detail.
The very fact that you, and I, had never heard of, or seen, the Milwaukee Art Museum is all the more reason for it to be made into an Architecture set. If Architecture sets are limited to buildings with which most people are familiar, the line would devolve into the pit of boredom that it's largely become. Very likely, not many people had heard of the Robie House, or Farnsworth, or even Fallingwater, but they were great sets, architecturally interesting, and perhaps people actually learned something - if only from seeing them on a store shelf. I wish TLG had the guts to make a set like this, but perhaps an Ideas set can show them the way.