Seems a bit early to me to speculate on why this happened. If I was going make some baseless speculation, it would be about how well the engineers are regulated.
Often it's the building companies that get skimpy on materials. The plans are checked and up to code, but the builders straight up embezzle. No one notices. (. . . Most times . . . .)
This building was completed in 1981. Either something gave way underneath it (supposedly residents had been complaining about water in the underground parking garage) or the building was a 40-year timebomb of shitty construction that finally manifested itself yesterday.
Saw a news story that said the lot/area this building was on may have been sinking at an unusually high rate over the last 20-30 years. Some research group detected it while conducting research on how rising sea levels might impact coastal areas in Miami, but their paper only mentioned it in passing in one sentence so nobody really noticed and it wasn't significant enough to them to raise any warnings because that wasn't the focus of their research so it didn't occur to them.
My baseless guess is subsidence of some kind. If it was that, there would have been signs the building management really should have noticed. It’ll all come out in the lawsuits I imagine.