I know exactly why.Great suggestions and I was genuinely surprised 5E didn't adopt the Bloodied mechanic because it's both really easy to track and really useful as a trigger for special abilities in both classes and monsters, and in both directions (i.e. your HP being low may trigger a monster ability etc.).
"Reeeee how can a Stone Golem be bloodied if it hasn't got any blood, reee"
Yeah, that was another Thing That Happened.