They aren’t, they are the foundational and distinguishing differences between the scifi and fantasy genres.
Fantasy doesn’t explain the “magic” or the “tech” it’s all handwaved and is just there as part of the story.
Scifi on the other hand, the technology is the foundation of the story, and the rest is built off of that.
Both can use parts of each other, but how the story is built is which dictates which is the primary category it should be in.
If you can’t understand something, and someone is trying to explain it, does that make them gatekeeping?
So using those non arbitrary definitions, it’s pretty easy to see DCC is fantasy, along with Star Trek and wars
Foundation, expanse, Robots, they all fall into the other.