> Looking at the surrounding building of the Sagrada, just makes me wonder again, what the hell happened to modern architecture.
To a certain extent: economics.
Beauty generally does not show up on a spreadsheet, and when it does it often adds cost. Glass costs less than steel, concrete, or stone, so it's lower CapEx to have glass towers. (Of course glass sucks as a thermal insulator, so your OpEx for heating/cooling may be higher.)
Glass is also not heavy, which is very important. (At least, relative to steel and brick.)
The modern glass curtain wall is popular because it is not load bearing and costs very little extra to hold up. High-rise steel frame was very expensive, and high-rise masonry basically impossible, because the frames also had to bear the weight of their own upper floors. The structural part of a modern skyscraper is basically floors cantilevering off a small concrete core, and the glass wall simply hangs off the cantilever.
To a certain extent: economics.
Beauty generally does not show up on a spreadsheet, and when it does it often adds cost. Glass costs less than steel, concrete, or stone, so it's lower CapEx to have glass towers. (Of course glass sucks as a thermal insulator, so your OpEx for heating/cooling may be higher.)