And to add to any of Alex's handpicked governors dying or better yet, executed on Alex's order, he also had to the real life time consuming process of sending another one of his officers to replace the recently deposed. I think this happened quite a few times in Asia Minor while Alex was still in Asia Proper due to conspiracies and such, but i only have Arrian as my source.

Just imagine if everytime (or just the rumour that) your faction leader died your entire empire would be immediately in revolt.