The fact that they released "time-line" and "ask questions" shows how few options they have at growing or expanding (or how few they've tried).
I think the greater concern for Facebook is that they have tried to expand their reach on several occasions in ways that would seem to favour them commercially, usually at the expense of people's privacy and/or making the user experience worse, but they have discovered that beyond a certain level of tolerance they will get enough pushback from their users to cancel the plans and they still have to eat the negative PR for a while. By your analogy, they want the trunk to keep growing, but the roots can't go any deeper to support it.
I think the greater concern for Facebook is that they have tried to expand their reach on several occasions in ways that would seem to favour them commercially, usually at the expense of people's privacy and/or making the user experience worse, but they have discovered that beyond a certain level of tolerance they will get enough pushback from their users to cancel the plans and they still have to eat the negative PR for a while. By your analogy, they want the trunk to keep growing, but the roots can't go any deeper to support it.