Simply because our founder and current Lead Developer was already well-versed and comfortable with Flash and ActionScript for both visual design and as a UI front-end for complex database-driven Web applications. Having started from that basis, it was always easier to keep updating and extending what we already had, rather than rewrite the entire Admin front-end from scratch. However, Development has lately started doing just that -- writing an all-new Admin in straight HTML/CSS/JS, which will probably go live within the year. This will eliminate some limitations with Flash/ActionScript that we've encountered and allow for much quicker and more frequent upgrades and tweaks to the Admin panels in the future.
