HP is abstract... except when it's not?

Something I've always wondered: If HP damage is supposed to be an abstract of wounds, fatigue, strain, etc. and you aren't actually in mortal danger until you cross that 0hp threshold...

Then why can't a good backrub heal HP damage?

No really, why is serious amounts of rest or magic required to heal what you're totally allowed (encouraged, even) to call stiff muscles (or the like) after a long fight?
Sure, you'll need magical healing energies or appropriate downtime to heal actual wounds, but HP damage above zero is never flat-out called actual wounds. And yet, a Heal skill-check can't cure HP?

Hit points do a good job as long as you don’t look too closely.

They’re a really poor simulation of health but it’s quick and easy, if you’re happy not thinking about it.

Think of cure spells more like a restoration of luck and general well-being. Maybe a CLW spell feels like a back-rub?
For reference, I just got home from a long day of physically demanding work, and I'm sitting on the couch feeling sore. I'll probably feel better after 12 or so hours of rest, but a "healing" spell would be quicker ;)

And yet, a Heal skill-check can't cure HP?

You can cure HP with Heal check, it takes 1 hour and it's DC 20 (or DC 24 without proper equipment). Just reflavor "treating deadly wounds" as "giving a backrub".

I do bruises, small cuts, stab wounds that failed to hit anything major and clotted pretty quickly, sprains that aren't bad enough to stop you in the moment of adrenaline...

Stuff that doesn't necessarily need penalties especially in battle, but which does need more medical treatment than you can provide with five minutes and a bandage. The reasoning behind the heal skill being difficult to use for actual HP is that it would make magical healing far, far less important. Magic healing is already not the best use of your turn in combat, and can be avoided between combat with cheap wands, so if you could do between combat healing with the rogue you would never bother to ally a cleric or spend gold on wands.

This is why I prefer a sort of Starfinder's system of hp and stamina. I would prefer a system where your hp never grows, and instead you just have a larger pool of stamina representing your energy. Damage would generally be done to the stamina pool, representing sorts of "near misses" that don't inflict any "real" damage by represent your characters energy and ability to continue fighting. I also like the realism of a system wherein your effectiveness decreases as you take damage, but that just leads to death spiral which are generally not fun despite being more realistic. You could then have certain abilities deal damage directly to hp, but it would need to be small amount since your actual hp pool is going to be small.

This would also enable you to heal stamina and hp separately, and allow stamina to be easy to heal but hp to be difficult.

HP are a game mechanic that is diconnected from reality. Trying to rationalize what they represent in the real world leads to madness. Almost nothing in this game makes sense in real life context.

It's a game mechanic. Treat it like a game mechanic.

-Skeld

Characters past like, level 2, are pretty much necessarily supernaturally durable, and there's a lot of ways to demonstrate that total hp more or less has to be at least reflective of raw damage soaking ability even if the system tells us that's not the only factor. I usually just let my players fluff the details any way they like.

I feel like the days of pretending our characters are not ridiculous anime mary sues who can just stand at ground zero for a nuclear detonation, are long past.

You would likely appreciate this blog posting:
http://thealexandrian.net/wordpress/1034/roleplaying-games/explaining-hit-p oints
"THE BEAUTIFUL ABSTRACTION"