Become? That assumes that AO was once well designed. There's been plenty of evidence over the years that that was never the case (to be fair, it was their first MMO, back when MMOs were fairly new things, so no-one having much of an idea how to build one well is hardly surprising).
A lot has been redone (all hail Macrosun!), but I get the impression that it's still pretty damn messy in there.