Quaint and Simple
Gosh, these tales are just filled with old-timey, quaint things like spinning (who even knows how to spin anymore?), agriculture (lots of farmer characters), and the feudal system. Because it's awesome having a hereditary monarchical government. And worrying about your children starving during a famine. Golly, we sure miss the good old days!
But all joking aside, there's not much to say about the writing style here, because it's clear that the Grimms weren't all that worried about, well, style. They had stories to tell, so they told them—no frills, no fluff. Just the facts, ma'am, with a healthy dose of matter-of-fact magic.