It’s incredibly useful in the game because it runs on the same liquid fuel that jet engines and rockets use (rockets also need oxidiser). It wouldn’t be as useful without that crossover.
Edit: I just realised that’s pretty much what’s happening here. The nuclear rocket uses hydrogen, and while it isn’t the most common rocket fuel these days hydrogen + oxidiser would be a functional rocket fuel. You could even run jets off it.
KSP also uses hydrogen fuel cells, which I think use liquid fuel to generate power. So it’s all pretty close.