D&D 5E Why are potions of healing so expensive?

[Rabulias]

And it seems to get glossed over a lot in some systems, like 13th age with Minions or a lot of 5th edition where monsters die at 0 but PCs get death saves. It's really #$%!% frustrating to not be able to question the bad guys if you miscalculate how tough they are.

D&D 5e Player's Handbook p.198:
Knocking a Creature Out
Sometimes an attacker wants to incapacitate a foe, rather than deal a killing blow. When an attacker reduces a creature to 0 hit points with a melee attack, the attacker can knock the creature out. The attacker can make this choice the instant the damage is dealt. The creature falls unconscious and is stable.

 

[Krachek]

DM can choose to roll death saves for a monster, or to keep him dying for a while.
A DM can also state that an action conclude to a death blow. Killing a creature outright.

 

[Krachek]

#2) It isn't an insult. But some players, including myself, like more of a sense of realism (including magic and it's limits) and consistency. Fighters shouldn't be able to fall 100 feet and live. The hero should not be functioning as if totally uninjured to 1% hp, and then taking a glancing blow and get knocked out. Potions that heal you should not be a few silver pieces because if they were every single person in the world would carry one.

Except in D&D land that commoner would only take an eight hour nap and the arm would be fixed, because everyone is Wolverine.

In DnD land commoner don’t suffer from any disease since there is no rules in the phb to contract disease in the day to day life.
There is no genetic problem, hereditary disease, since it is not note in character creation.

On the other hand, commoner frequently died being roasted by a dragon, or thorn apart by a troll.