A lot of GMs focus on story and don't even care about the mechanics/rules side of stuff within Realm Works. They have it mostly memorized, or have someone in the gaming group that is the resident rules quoter. You know, the guy who proclaims "If you look on page XX of rulebook YY, you'll see in the third paragraph that blah blah blah."
A lot of GMs focus on the story and only want the rules when they truly need it. So they don't want the rules cluttering everything up all the time. It's just like running the game. Focus on the story, then go pull out the book (or check the rules entry in RW) when it's actually needed. There are a few folks above that advocate this approach.
A lot of GMs use story content with different game systems than it was originally written for. There are lots of D&D adventures being used with Pathfinder and different versions of D&D. There are lots of Pathfinder adventures being used with D&D5E. So keeping the rules distinct from the story is of critical importance here.
It's our expectation that lots of content will be published/shared for RW that will be game system neutral, plus a lot more will be published for one game system and used with other game systems. The ability to do this will be greatly enhanced by having a clean separation between the story and the rules, which will encourage more users to do this. So it will become a self-fueling model.
When we thought about the optimal long-term approach, as opposed to how everyone does stuff today, making the separation was clearly better for the majority of users. So that's the approach we took. It's something we adopted from the very early days, but I honestly can't remember whether it was in the first Beta that @ShadowChemosh got his hands on.
So that's why we did it. The good thing is that, if you don't like it, RW gives you the flexibility to do whatever you want instead. If you want to move everything over to the Story side, go for it. You can copy the categories, move them to the story side, and be off and running. Or you can roll everything custom for exactly what you want. It's entirely your call.