I was under the impression that Malak did what he did to become the supreme ruler of the galaxy.
Seems like they all have that goal but there are other better ways of doing that than destroying everything because if you blow up everything, what is left to rule over? I would think itd be better to scare people and make them "think" youre gonna blow them up most of the time and just pick and chose when it would be best to actually destroy something, like when it would benefit you somehow. Thats why these badguys who show no mercy and kill/destroy everything for the sake of it dont last. Its better to just keep people guessing about your intentions or make them at least think youre doing everything for a good reason and their benefit.