This dishwasher spends 10 minutes washing, then drains and fills again before it opens that dispenser.
So if you use a detergent pod, those first 10 minutes of washing will be done with nothing but water.
Now, that can still do a lot! And you may be having fine results with your pods. But by not tackling the fats and oils in the first fill, the detergent has to work harder in the main wash cycle. Encapsulating oil particles uses it up and makes it less effective.