They would stop using it because they perceive its value as a useful tool is fast diminishing. When they were a neutral forum, they were valuable. As people begin to understand blocking and shadowbanning, they find it less useful. Pure expectancy Theory. If you cannot count on a result you will not use it. When you begin to believe that your Tweet or Facebook post just goes out into the ozone and nobody sees it, and that fact is hidden from you, you will not use it much longer. People have to believe that there is a correlation between their efforts and an outcome that they want. If the outcome I want is to communicate a political message, and I cannot determine whether that outcome happens, and worse, its deliberately frustrated and hidden from me, I’ll walk away as will millions of others.
Facebook is already a Dead Man Walking.
Why are you defending Facebook Google and Twitter so hard? That seems a little odd.
Facebook may have peaked, but that doesn't mean that young people are any less glued to their phones. It doesn't matter if people use less of FB, and switch to SnapChat (or whatever is currently trendy) if the same group of California techies (whose strings are pulled by the same set of venture capitalists) still control who does and who doesn't get to speak to a wide audience.