Sadsquatch is an awesome name but, as @lgriffin points out, Christy Mason totally wasted it, tweeting only once, six months ago, in search of banking advice.
Because of how Twitter is set up, it can be hard to oust inactive users once they've established their username. Unless you know someone on the inside, your odds of setting up at @sadsquatch as a depressive northwestern yeti are slim. And there are plenty of other potentially brilliant handles locked up in the same bind.
A few of the most pressing cases:
Tragically, @Faceeater completely missed the Great Face-Eating Scare of 2012. The loss to Twitter as a platform is incalculable.