That's usually because writing "active evil" in a way that is compelling is really hard. They either need to have a crippling weakness to allow the story to drag on, which diminishes any real threatening aura they may have, or are a constant villain of inconsistent writing that keeps them making dumb mistakes that makes it impossible to take them seriously to begin with.

And even if you succeed, you have the final risk of "then why is there even a story" where you have to somehow justify them not just finishing the heroes and ending the story every time.

Griffith is a rare example of an "Active Evil" who is competently written and generally avoids all the pitfalls that would plague the character in any other work. But look at how high a bar that is, how many writers are even within a throwing distance of Berserk?

Honestly, its one of the few ways Western Comics has the leg up. Because things can just be decanonized on a whim, or just serialized for a very short "what if" run from the outset. So they can take villains and just make them act like they want to win for once, and not have to worry about the next issue that follows it.