Why does Daniel Marshall still use foam block/glycerine hydration systems?
Daniel Marshall Inc. has in fact, used the crystal gel type beads in their humidifiers in the past.
Please keep in mind that setting up a humidor is more like a science rather than a simple plug and play device. It takes time to set up your humidor, it may, in some cases, take a few weeks until your humidor is stable at the RH you are comfortable.
They choose to continue using what is essentially the Credo Humidifier for a few main reasons. The Credo system is simply the longest actively used way to humidify your cigars within your humidor. It is also highly flexible, if you need to bump up your humidity, simply add a little more distilled water. If you need to reduce the humidity, leave the humidifier out of the humidor for a day (then re-install)
If you would like further information on this, you may contact Daniel Marshall via here.