At this point, Facebook has simply waited entirely too long, and the likelihood of any pivot working for a company of their size is basically nonexistent.
You could also say that "they won" and there's no where to go but down now.
Nothing can grow forever and things that try are known, in the biological domain, as cancers or infestations. There's quite a few corporations that "won" their market, so they're primed for a decline-- if you can still even call it that after enough people made more money than god and retired.
Because exactly as you said: Facebook "won" the social network game several years ago: Everybody was in there. From there the only thing it could do to try to milk more profits was to bring it down.
Instead, we've got IRC or Usenet that, years and years after their "peak", they are still going well and good. Gone are the "ethernal septembers" and most of spam. And the protocol and networks (that matter for the people using it) are still in there.
They haven’t monetized Messenger or WhatsApp much either. Maybe they can’t or it won’t ever be enough. Less than billions in profit won’t help much. Which does make them having won and are now going down seem more correct.
They "sort-of" did. The Open Compute Project (https://www.opencompute.org/) is an effort in which Facebook played a major role. The motivation, for them, is to break free of the shackles put on them by computing and networking equipment vendors (like Cisco). Facebook is big enough that they could design their own stuff, and try to make it a commodity which, as a side-effect, allows others to get involved and benefit from as well. It's hard to say how well this has worked but it was "an initiative".
b) Facebook isn't really pivoting to metaverse any more than Apple is pivoting to services. It's an additional revenue stream alongside their existing ones which are still very healthy and lucrative.
This strategy has run it's course. Regulators are keen to weaken FB and will obstruct further acquisitions. Acquisition targets know they can beat FB in the long run and will no longer agree to be purchased.
Today, nothing is chronological, profiles are (somewhat) public facing, people just posts links, photos has basically moved to instagram, messaging has moved to whatsapp, and events hasn't changed a bit. Plus there's a ton of other new features that dilute the tool.
The first pivot was into Photos. A mini pivot, but an important one as being a glorified contact list and blog was on the way out.
Then they saw another competitor rising, so they bought it to ride its lifecycle. Instagram.
Then into Messaging, with messenger and WhatsApp. Most people I know use one or both of these and not Facebook.
There have been other smaller pivots to stay relevant overall, even if any one piece of the business is dying, and I think that’s good business practice.
Whether the meta verse turns out to be the next wave or not is essentially their current bet.