Sorry for what I said about your mother
I wish people had to give a reason, at least then I'd know and wouldn't be wondering what I've done. I hate being silently booted, it's happened to me a few times and I don't know why. There is no notification that someone has removed you, so unless you have a small number of friends you don't notice until months later. By that time it doesn't seem worth getting in contact with them to find out why, and I'm reluctant to resend an invite if they removed me.
My guess is it's the last of your answers: I am boring and pointless. Though it's not exactly as if there is a limit on how many friends you can have, I don't see how my silent and never-updated Facebook profile is hurting anyone's friend list. Truth is I hate Facebook and don't want to use it, but people kept inviting me, so I joined. The only thing I've ever used it for is to accept a friend invite. In total I've spent about 20 mins on the website in the last year.