The network effect is still there, they have billions of users who are on Facebook because friends and family are on Facebook.

Are they really? perhaps it is just my social circle - but I've observed most of the group traffic having moved to SMS and WhatsApp. While WhatsApp is a meta product, the economics are extremely different.

There are really just a handful of people from my extended social circles still actively posting to FB/Instagram and that traffic is mostly drowned out by slop content.