Yep.... nitrate factories.
When you consider the live rock and sand in the system, more than enough bacterial population area exists to handle the biological needs of a properly stocked reef tank.
All wet/dry filters become is a place for nitrate reducing wastes to accumulate and cause issues.
The new trend is towards eliminating filter media all together to eliminate places for debris to build up and combining flow to help bacteria do it's job and prevent detritous from accumulating in dead spots, a proper cleanup crew to break down waste products into dissolved organics, and protein skimming to yank those dissolved organics out of suspension in the water column. All this together is known as the Berlin method.
By and large, it's gained acceptance industry wide, endorsed by Marine Gods like Fenner, Knopp, etc and is almost always employed in public aquariums and large scale systems.