Sometimes game designers make terrible mistakes and think that their pet idea is way better than everybody else thinks it is. Sometimes they change things just to be changing things and muck everything up. Then there are the times when they simply give up and say "Well, we know this system is bad, but fixing it is hard, so we aren't going to bother."
In short Wizards has decided that DnD Next should return to the old system where either you have a cleric to heal you in the party or you don't get healed. Have a three person party? I guess one of you is a cleric, because if nobody is then you can't play reasonably at all. Wait, none of you wants to be shoehorned into casting only healing spells and being forced to roleplay "Please give me my spells God, even though I am so unworthy."? Too bad, because somebody has to play a pious healbot, no way around it. Other classes are entirely optional but the cleric is entirely mandatory.
It makes my head explode. There are a crazy variety of ways to get around the absolute necessity of faith based healing and clerics in particular. You could, for example, set it up so that characters have a pool of temporary hit points that come back after a short rest so that they avoid taking real damage a lot of the time. You could change the lore slightly so that other classes can heal, or so that everyone with levels has healing capability! One of the problems they worry about is people wanting 'realism' but apparently people are willing to accept adventurers who get stabbed by a sword 15 times and walk away from it so I think they will be able to deal with lore that says that adventurers heal really quickly.
I completely get that DnD is a cooperative game where people play together and they try to fill roles. Some people will focus on being tough, others on killing the enemies, still others on stealth, diplomacy, or whatever. This mimics real world team setup from military to science to commerce, so it makes sense. Unfortunately this sets up the game so that all the roles are flexible *except* healing so you simply have to have that cleric - you can't have a fighter who dips into healing a bit to cover that eventuality.
What DnD Next actually needs is a solid healing mechanism that doesn't involve any class at all. If people want to play a character that defends their allies then well and good - clerics having solid defensive options in combat like adding on temporary hit points or increasing armour class for their allies is a great idea. That way clerics are like the other classes in that they have a particular specialization and iconic abilities but aren't required to be present for the game to make any sense.