They've tried it and Hickson just isn't as good as most people in Ohio think he is. No one outside of LJ is consistent threat and replacing Mike Brown won't change that.
Hickson is a distinctly ordinary player but he has a good effect on the Cavs pick and roll defense, transition defense and is very talented complementary offensive player (as well as being a decent rebounder).
Simply put, unlike Jamison or Shaq or Big Z, Hickson isn't a major defensive liability. He is about average. A little vulnerable defending the post and misses the odd defensive rotation but his good defensive contributions add slightly more than his negatives detract.
So, a fairly mediocre defender ... but that is better than being a major liability (Jamison, Shaq, Ilgauskas).