In the ~8 years since I worked there, Zuckerberg announced that we'd all be spending our 8 hour workdays in the Metaverse, and when that didn't work out, he pivoted to crypto currency.
He's just trend-chasing, like all the other executives who are afraid of being left behind as their flagship product bleeds users...
Across all products, maybe not - Instagram appeals to a younger demographic, especially since they turned it into a TikTok clone. And WhatsApp is pretty ubiquitous outside of the US (even if it is more used as a free SMS replacement than an actual social network).
Growth in monthly actives across Facebook seems to have slowed but is still increasing--not bleeding users--from data I found through Q4 2023.
With 3 billion monthly actives and China being excluded, it's hard to expect a ton of growth since it is a major fraction of the remaining world population. There are bots etc. but they are one of the stricter networks with requiring photos of your ID and stuff a lot more often than others.
Keep in mind that Meta pulls something of a fast one here, because a lot of instagram accounts end up creating an attached Facebook account (so that they can share Reels across both platforms). I don't have current insider information, but as of 2019 they were heavily using instagram sign-ups to shore up the Facebook numbers.
He's just trend-chasing, like all the other executives who are afraid of being left behind as their flagship product bleeds users...