As with most disasters, I suspect it is the alignment of several situations that, by themselves would not have caused the collapse, but together led to the disaster.
First, the building was build in 1981. This means it was designed using techniques from the late 1970s. No computer design. No computer stress analysis. All done by hand. If anything, IMO, this would have resulted in it being overdesigned, as the computer design systems are much better at minimizing the design based on cost. With manual design, you produce a design, run the calculations to prove it. Repeat as necessary, but the iteration is done by hand on paper and is tine (and money) consuming. It was much more common to overdesign in those days than to optimize for material cost.
This was also a time of a large economic recession. Cheap Chinese steel wasn’t available, but Cheap Japanese steel was. However, at that time, the Japanese structural steel on the market was cheaper and of higher quality than domestic steel (the steel industry was looking for protections from the government). In the 1970s, steel in the US was being made in mills that produced the steel used in World War One (as well as WWII). The design likely was based on the quality of the domestic steel (which had been used for decades and was well understood). In all likelihood, if cheaper steel was used, it would have been of better quality than what the design was based on.
When I was in Engineering School, I had a roommate from West Palm Beach. This was the late 70s. He told me that the construction of condos along the beachfront from Miami north was out of control and since, at that time, had not had a serious hurricane hit Miami in 20 years or so, he expected a lot of those structures to fail when a big one hit. He was wrong. This structure survived 40 years. In the past 20, south Florida has been hit multiple times by severe hurricanes and none of those condos were blown away (including this one).
My bet on the most significant contributing factor is building modifications. Walls being removed or modified, ceilings raised, whatever. Probably within the past two years or so. I suspect that if an unusual event (explosion, enormous party, truck running into the building, whatever) had occurred, at least rumors of such would have hit the internet. That suggests the structure had been failing for some time (like the DeSoto bridge) and the evidence was just being ignored.
If I was 40 years younger with a newly-minted Engineering degree, I would start a Structural Inspection firm. I suspect, in the near future, that business will be pretty good.