Mobile, mobile, mobile. In 2010 everybody would hit Facebook multiple times a day from their workplace. In 2017 nobody in the developed world uses their work computer to access Facebook, they pop open the Facebook app on their phone or have it open 24/7 on their home computer. The people left doing the Google -> Facebook routine are those in developing countries who either don't have mobile phones or don't have app-capable mobile phones.
If they could make an official Facebook app less resource hogging, more user-friendly and usable on older mobile phones, they would be back in the game. But their app is probably the worst app you can have on your phone. It's terrible, slow and a joke. I would expect such an app from Verizon or GoDaddy, not from Facebook.
