My practicing architect friend states that those buildings go down like dominos if one structural column is compromised. I got the impression there isn't any redundancy built into the structure. I'm very familiar with spalling and seeing rebar exposed and supports crumbling because I live in the rust belt where we apply millions of tons of salt to our roads in the winter. I've seen retaining walls suffer the same fate as salt creeps into the structure.
My amateurish guess is that columns were compromised and could not take movement/subsidence. So was the foundation the problem or the spalling? Likely a combination.
There is redundancy, you lose one column, you probably don't have catastrophic issues, but if you have a bunch of columns that are weaker due to weathering, and one fails, while a number of other ones have lost their redundant capacity, this is a big problem. And generally, one element just doesn't go bye-bye without others getting weakened by whatever weakened the initial element.
Foundations
can fail spontaneously, but it isn't terribly common, even in Florida, with limestone that has holes in it.