We do not delete accounts because a huge batch of posts suddenly disappearing could very easily make some threads difficult to follow, confusing people reading them for whatever reason (perhaps an old thread with interesting/useful info). I'm personally a strong believer in maintaining community history as purely as possible, and hundreds of posts vanishing without any evidence that they were ever there is not the best way of achieving that.
It's also a pain because when you delete a vBulletin account, the posts are not
deleted -- they are simply associated with the 'Guest' account. Deleting the posts themselves requires the script to go through the whole database and look for any matches, which can be a little stressful on the server and also requires us to do various other things such as rebuild the forum search indexes and post counters. All very inconvenient and disruptive.
If you didn't want certain information to be available on the web then it's really your own responsibility for not thinking when you posted it. You're free to edit out information that you don't want people to find, but in all likelihood it'll continue to persist on the internet for a very long time as services like Web Archive
exist, as well as Google's own tendency to not remove the meta information in its result pages for a long time.
If it's just an employer worry, editing your name out of your old posts should be just as effective as deletion would be. We can also rename your forum account if you want us to.