The King's magicians are classic enablers. Though they only appear briefly in the story, the magicians have a powerful effect, primarily due to their unique ability to give a power-hungry king the illusion of more power.
And they're creepy, too. What's with all the shuffle-dufflin'?
As they bend over their pot of ingredients, they're like some weird version of the already weird witches in Macbeth. Except, unlike the witches, they're so poor at predictions they can't even say what their own oobleck will become or do. They lack even the illusion of withheld knowledge.
All in all, the magicians are the perfect example of why we shouldn't be fooled by novel things that come from people with a fancy title. They're often just a bunch of goop.
Okay, maybe that's not fair. There's another angle to this, too. Like all of the King's other subjects, the magicians feel obligated to do what the King asks. Maybe their dull expressions don't come from a lack of intelligence; maybe they're just slaves.
One last thing: did you notice that the magicians speak in rhyme? We knew Seuss couldn't make the switch full on. Once you go rhyme...