Small Or Seemingly Insignificant Details with Lore Background / Reasoning

I just learned that Land Raiders are named for the inventor/discoverer Arkhan Land, not because it is a land-based vehicle.

What are other small or seemingly insignificant details that might, surprisingly, be explained by something in the lore?

Like, why are bolters usually red? Why does High Gothic sound kind of like Latin? Why do Harlequins look like medieval jesters? Etc

I feel like most of the answers will be, "Because it looked/sounded cool" but if I find out the reason Raven Guard marines have emo haircuts is that blocking one eye with their hair preserves partial night vision, that'll just make my day.