I know very little about the actual job of an architect, but I think new architectural design trends have a lot to do with the tools that are used to draw buildings. Being an architect used to require strong drawing and mental modelling abilities. Those two would have an impact on the aesthetics of the buildings.

Another factor is the way we move around. When you walk, you have the time to see details. Do architects nowadays spend many hours walking in cities every week?

Lastly, the cost of manual work probably had a big impact. Builders probably contributed a lot of the beauty that can be seen in old buildings, also because drawings used to be less precise.