Pretty much well summed up! Saves me doing it
Theres also a certain narrative to it. 40k in general thrives on certain level of tragedy. Sacrifice and martyrdom are held up as virtues by the entirety of the Astartes, far more so than chapter pride. And not all sacrifice is found on the battlefield, after all.
All in all, the idea of a mighty warrior separated from his brothers, fighting insidious threats half way across the galaxy and never able to return home sounds like just the sort of Greek tragedy 40k is built on