To start taking users away from Facebook, it needs to be sufficiently better than them to overcome their network effects. Which are substantial. Some of the features that I'd count as "better" would be laughable coming from Google:

• more social, less monetised for ads
• not sending traffic to fascist tech bros
• just show me my friends' updates, don't fuck around with them with an algorithm
• I want my "work network", "social network" and "email" to be from different companies, so none know too much about me

In addition:

• actually advertise what's better about them, so people will move. "Circles" was the most confusing shit I'd ever seen

• some of the prioritisation in FB was exactly backwards for me; I want to see more distant friends' updates more often, since I see my local friends to keep up with them. I want to see friends that post less often prioritised over attention seekers that post every time they fart. That might be "algorithm" tho; feed you tidbits to keep you scrolling

Then tack on the marketing hype cycle presenting it like it never existed before and it's some revolutionary technology.