In 2011, Facebook was good at its job, with a chronological news feed, meaningful notifications, and a messenger paradigm that worked much like AIM in the early 2000s -- you could see who was online, away, go invisible, etc. In 2018, Facebook has lost all of those positives, and with it a lot of user engagement, all for the sake of cramming the maximum number of ads down the users throats. And I'm not even getting into the nasty dark UX patterns, like hiding the ability to delete your profile (seriously, there isn't a link to do this anywhere on the site -- you need to search Google for it and they change the link all the time to break external guides) and showing random pictures of "friends who will miss you if you leave!" when you try to delete your account. I don't think your average user would mind leaving Facebook much if there was any actual alternative.
This is just a minor quibble to lambda_lover's point, which still stands. Facebook may understand it's job is to shove as many ads in its users' faces as they will tolerate, but that's not why users use its app. It's users view its job as being useful to them, and being bad at that makes makes FB vulnerable to competitors or even just general dissatisfaction.
Every developer on Earth could leave Facebook and it would not make the experience of using fb any worse. Facebook is not a software platform, it’s an ad platform.
If anything fb would get better if we stopped targeting it.
When the Chrome came along, Firefox already put a dent in IE market share and it already became socially unacceptable for techies to use IE but regular people still used IE so the devs were forced to make sure that everything works perfectly on IE too. For the masses, thanks to the developers, IE displayed the websites just fine up until the bitter end.
Friends didn't let friends use IE and it was killed.
It’s far from dead, although we’re finally seeing Edge and Firefox rise a bit more sharply.
Slow-moving, heavily regulated corps with lots of internal legacy apps simply cannot use Chrome with its frequent feature deprecation, weak management, and constant desire to send telemetry and who knows what else to Google servers.
:)