Because Oden has not asked and WB didn't know.
Ace got killed Because of his own stupidity after getting saved
WB did know cause ace told him the country was fuck and how could Oden ask when he was dead.
His excuse was war vs him and Kaido would be to much people dying while th people there every day dying for the last 20 years .
Side note luffy and company fought 2 yonko there , where was this big death count aside from the solders on both sides.
Ace still died in end even if it was because of his stupidity so they lost and got fuck up in end for nothing .