That's because the drying is only the first step.
Hang them in a cool dark airy place until the small bud stems snap when bent.
Then remove all the buds from the stems and place them in a glass jar with a tight lid.
Every day, open the jar and feel the buds. They will feel more moist than they did when you closed the jar. Leave the jar open for half an hour, then close it again.
Repeat until you cannot feel a difference in moisture from day to day.
Then seal tightly and put in a cool dark place for 2 or more weeks.
This is called curing, and you have to do it, or your buds will be harsh. Dehumidifier is unnecessary.