What's a more intriguing question is why he turned on Michael.
Never explained...like so much else in GFIII.
It is kind of, sort of explained, that is as well as anything in GF III is, For whatever reason he was beholden to one of the Immobiliare guys who opposed Michael. As Michael rightly said he had a lot of fingers in a lot of pies. I think Altobello knew that he either turned on Michael or he would be dead.
"Io sono stanco, sono imbigliato, and I wan't everyone here to know, there ain't gonna be no trouble from me..Don Corleone..Cicc' a port!"
