Hmm I don't know.
I mean, yeah XD absolutely failed, but when Adobe released it in 2016 Figma wasn't nearly as popular as it is today.
My guess is when Adobe decided to build XD (a couple of years before 2016) they were trying to compete with Sketch. So they probably missed the collaborative web-based aspect that made Figma popular.
And maybe XD was just an underbudgeted experiment to test the waters, not a serious product like Photoshop.
Edit:
I just realized Figma was released in 2016. I was probably thinking of InVision.
https://www.pcgamer.com/mark-zuckerberg-spent-dollar10b-on-t...
even in the very unlikely event they were able to build a product with feature parity, with little operational blunder, on budget/on time, they still need to market it and get enough paying users to match the $400 million in revenue per year which Figma currently makes.