[Jeff Chandler]

I can think of three causes.

1.) The building was improperly built because of graft.

2.) The building was weakened by nearby construction.

3.) The building was deliberately sabotaged .

[Jeff Chandler]

I can think of four causes.

1.) The building was improperly built because of graft.

2.) The building was weakened by nearby construction.

3.) The building was deliberately sabotaged.

4.) Sinkhole.

[Lonesome in Massachussets]

4.) Construction on a barrier island.

https://www.nbcnews.com/news/us-news/cause-miami-condo-collapse-unclear-experts-say-barrier-islands-present-n1272316

[BenLurkin]

The building was forty years old. The concrete and rebar may have corroded from long term exposure to saltwater laden air.

Poor construction probably contributed.

Just my guess.

[Fledermaus]

Sink hole

[sevinufnine]

4) Was built on “reclaimed” wetlands. Meaning it was ocean before they decided to make it a land mass.

5) What is called “concrete cancer”. The sea/salt can cause corrosion to the rebar inside and make it very, unstable. Since it was already sinking slowly, that would make this situation worse.