It's that way because the test initially evolved from fixed wing education and testing materials and it's not been modified to be more specific to SUAS. And as
@Robert Prior pointed out, Part 107 does include fixed-wing drones. But even considering that, you'll find quite a bit of content that's not really relevant - airport traffic patterns, meteorology reports, aerodynamics, ... The Part 107 test could certainly use an overall revision.
I had a Part 61 certificate from years ago, so most of that content was familiar in my case. If you work through the practice tests you'll find online, you'll probably pick up most of the content that might appear on the test and do just fine. For now, it's just something we have to put up with.