Because it is not commonplace in most instances. Perhaps at high level this might not be the case but in the world in general I don't expect them to expect healing.
Ordinary intelligence should lead one to conclude a party with spellcasters will bring their fallen ally back immediately unless you take that fallen ally down.
Yes that point was made earlier. I was not assuming melee combat necessarily. But of course, if it's melee, it's even easier.
This is a nice simple way to go, and actually checks with the math. So if you look at the CR scale from the calculator, every CR bump is +6 DPR. The "average" character gains a d8 hitpoints (5 on average), with +2 from con (in my experience most players get a 14 con), so that's +7 HP per level. So you can see that with every CR the monster is in theory getting a little less deadly damagewise. This of course is not even factoring in better healing, other buffs, conditions, etc etc.
"The fighter's down and the path is clear! Get the wizard before he throws another fireball!"
That's a lot of assumptions there, all of which are going the pcs' way. You're assuming someone in the group has healing word and spell slots, that they aren't going to use their bonus action for something else, that there's only one attack available to spend on the fallen pc, that- once healed of around 5-10 hp- the pc won't just drop again in one hit, etc. These things aren't always true, and they are rarely all true. Or if they are, your encounters aren't using enough monsters to be as challenging as you want.
There's no CdG in 5e.
I see the +1 damage per CR as an easy way to get damage closer to the DMG DPR table* without having to recalculate everything. Not perfect, but pretty close.
