So let's say we have a game in which (on average) 4-6 characters go adventuring and, over the course of the day, their resources are whittled down.
Sometimes (actually quite often) those resources are asymmetrically depleted for one character. This creates a strong incentive for the group as a whole to stop and replenish, decreasing their chances of failing any given challenge and--more importantly--keeping the player of said character engaged rather than on the sidelines.
How do you solve that problem for all groups in a way that doesn't make any one type of character obligatory?
Different characters have different resources. Barbarians have daily rages. Wizards and Clerics have daily spells. The thing is, those resources are specific to those classes, and don't largely affect the group as a whole. The key to making sure that those don't become a problem is giving every class at-will abilities to fall back on so that they're still competent and able to contribute even when their limited resources have run out. They've already done this.
Then, there are resources, like hit points, that everyone has. The difference there is that even though every character has hit points and needs to get them back when they're lost, only certain classes, such as the cleric, are given the ability to replenish them. Wizards are self-sufficient when it comes to their spells. The same goes for barbarians and rages, fighters and surges, etc. They don't depend on someone else to get those back, they just rest, and they can continue to adventure even after those resources have run out. The same is not true of hit points. When those run out, your character is out of play (either dead or unconscious) and you don't get all of your hit points back by resting, they recover very slowly. When a barbarian runs out of rages or a wizard out of spells, the game doesn't come to a screeching halt. When someone's hit points run out, the game
does come to a screeching halt. To avoid this, people load up on magical healing.
4e solved these problems by giving everyone self-healing and by having hit points recover completely with rest. The alternative is either forcing someone to play a healer, or stocking up on wands of cure light wounds and healing completely after every battle anyway. I don't know about everyone else, but I'd rather just dispense with the wands and let people heal completely with a long rest. If we
really wanted to be realistic about it, people would needs days, even weeks of rest after suffering injuries in battle. Do you really want your game to be THAT realistic? Do you really want to have your character be hospitalized after every battle if no magical healing is available? I don't!