It was the biggest new IP launch ever, wasn't it? I guess sales numbers for Destiny 2 fell off hard.
Not at all. D2 outsold the original Destiny, 3 month after release in unit sales.
"The company also said Call of Duty: WWII had earned $1 billion in global sales, and that Destiny 2 had already outsold its predecessor, in terms of units sold."
https://www.polygon.com/2017/12/20/16801308/call-of-duty-ww2-sales-activision-destiny-2