This is a real question - Why would you want it to work the other way?
Because it would fit better with the rest of the system. For example, let's say you have a PC with 100 hit points and a PC with 10 hit points.
Which is more likely to be taken out by an ogre's club? Okay, now which is more likely to be taken out by a death spell? Why would the 10 hp guy be more likely to resist the spell? Be a bit ludicrous, wouldn't it?
Of course, a death spell could also just deal damage. Then that'd fit. But a sleep spell or paralyzation spell or any number of things can assess the same way. If your save or suck spell takes someone out who has low hit points, then that's absolutely fine. Not like a damaging spell couldn't also have done so, even if (optimally) it's less likely to do so. But taking someone out with 100 hit points? That's pretty crazy unless it's a very high level spell.
I can see the making woulds affect other things would simulate the real world.
That's an added bonus, but you can argue any which way.
But revering it would make heroes that hang on in the face of adversity that would simulate a good book or movie. Wouldn't that also be a good goal?
Heroes that hang on in the face of adversity, but fall to a random goblin hit? I think you're missing that your current hit points also represent your ability to hang on in the face of adversity. So the hero who hangs on in the face of adversity _has more hit points_.
Mechanically, lesser saves when wounded could lead to a death spiral.
Are lower hit points when wounded also a death spiral? I mean, each hit is much more likely to take you out.
If people get a saving throw bonus from having hit points, then it's not a death spiral. It's improved saving throws over what we have now. A life spiral, if you will, because now it discourages people to throw out their dangerous effects early on, encouraging combat to last a little bit longer, be a little less decided by that first round nova.