[Darryl Ramm]

Because the unisntaller is broken on Mavericks.

But in general you should avoid doing in-situ upgrades on OS X, and Avid warns you not to. They can be too flakey. It's better to clone an archive of your old systems and do a complete new clean OS X install and then reinstall the right versions of apps and plugins clean on that OS X release. You can use system migration assistant to bring over user files, but not apps or drivers. Even better buy a new boot/system drive and install everything new to that in a USB caddy or similar and only install that inside the Mac, or clone it to the internal drive if everything works. A good clean out like that every few years is probably worth doing anyhow.