Hi, it's likely been disabled as it's been subject to malware attacks for years, after dozens of patches...
Out-of-date versions of Adobe Flash Player do not include the latest security updates and will be disabled to help keep your Mac secure. If Safari 5.1.7 or Leopard Security Update 2012-003 detects an out-of-date version of Flash Player on your system, you will see a dialog informing you that Flash Player has been disabled. The dialog provides the option to go directly to Adobe's website, where you can download and install an updated version of Flash Player.
If you need to re-enable an out-of-date version of Flash Player, you can do the following:
1. Navigate to the /Library/Internet Plug-Ins (Disabled) folder.
2. Drag "Flash Player.plugin" into /Library/Internet Plug-Ins.
3. If the browser is running, quit and restart it.
Two bugs, one affecting Apple's Mac platform and another attacking Microsoft's Windows, exploit certain Flash player vulnerabilities to install malware onto users' systems, reports ArsTechnica. While users of other operating systems like Linux have yet to report attacks, Adobe's advisory notes the exploit affects all platforms.
Designated as CVE-2013-0634, the first vulnerability targets the Safari and Firefox Web browsers running on OS X, and is also being used as a trojan to deploy Microsoft Word documents containing malware. For Mac users, the flaw affects Adobe Flash Player version 11.5.502.146 or earlier.