Well, apart from some OS and database problems, nate said:

The problem isn't an infrastructure issue, however -- and speaking as one of the handful of people who've had a hand in developing the site's software: It's our own gosh-darn fault. Perlmonks is WAY more complex than when it originally launched. It does a crapload of perl evals and sql queries per page. It's vulnerable to resource hogs. Searching can cripple the database. And right now, I don't think we're gonna fix these problems any time soon.

So i thought i'd look into the code only to find out it is very complex and unpenetrable.

A redesign allows you to create things The Right Way™ from the beginning on, and that's one big advantage.