Movable Type never had the foothold that Wordpress has developed over the years.

Once you reach a certain size, inertia alone will allow you to survive for a very long time, even making bad mistakes. Digg died because it was still small enough that a mistake could kill it; Reddit is now so big that the exact same mistakes (or even worse ones) will just not stop it. Same for Twitter or Facebook. Wordpress is way past the size where it will take something more than an isolated legal case to cut it to size.