Instagram is how they are making money
FB did $40B, $55B, and ~$68B in revenue for 2017-2019. Instagram has been ~$4B, $7B, and ~$15B for 2017-2019. IG as a part of revenue has certainly grown from ~10% to ~22%. However it’ll be a while before it gets to be the majority. IG has possibly had its biggest growth period by now and has already had a lot of ads added.
I wouldn’t bet against it topping 1/3 revenue in 2021. Hard to predict that and beyond that. FB may also [begin to] monetize FBM and/or WhatsApp or something else by 2022.