Marketing.... Pure Marketing
More specifically Millenial marketing.
Because it's too difficult to toss the pod in the drum. One needs a college diploma to do that, so now people don't need to think, just toss the pod in the drawer.
In no time, detergent manufacturers will create a new technology, even "easier" to use, but unfortunately "a little bit" more expensive (just 25x the price).
The detergent will be a powder with a scoop in the box, then a second box with the pods. The user needs to carefully dose the powder detergent using the scoop, then use a scale to make sure the dose is accurate for each pod, then fill each of the the pods (10 pods if you have a large load, 4 pods for small loads). Then you place the pod in the dispenser drawer.
But don't worry, this new technology is much better than simply dosing the powder and pouring it in the dispenser. Because the dispenser has an exclusive place to put the pod and also because our grandparents used to do that, so, if it's different, it's obviously much better than jurassic things our grandparents did.