I'm assuming you're talking about that. Like it was mentioned there are other eras.
I would say that was the golden era of architecture, there were classic iconic architects who controlled the whole process from the genesis of the design through construction through choosing the furniture. Since then architecture/architects have been getting diluted. The contractor actually has more power in terms of how things actually get built so there really isn't a strong design style.
Also it's clean, simple with strong lines. So appeals to a majority of people.
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