I wonder why there hasn't been a food-related challenge-reward perk?

We've already got Camel of the Mojave for water drinks.

Since it is a challenge perk, it doesn't have to take up a level perk slot. Hooray.

Here are a few ideas

Vegetarian- Consume X fruits and vegetables

Carnivore- Consume X meats (including human flesh)

Junk Meal- Consume X processed foods

Forager- Consume X of any foods

IMO Forager should reward a perk that is bit less effective than a specialized diet like that of mainly vegetables or mainly meats. Of course once you get rank one of one of the specialized diets you can get the other, but you can still get the Forager reward perk.

I don't really care for those sorts of achievements or any achievements, really, but especially ones that reward perks. They're little more than free handouts as it's often something you're going to do anyways without even trying.

I thought the learn by doing was Elder Scrolls thing, I personally don't want any perk to be forced onto my character for simply playing the game. (*cough*OWB*cough*)
I'd rather they stick to the perk:2levels formula, you want something to make your character better? Then you gotta choose carefully.
Free perks should exist, but they should be something you have to work for, like Gecko Skinning in Fallout 2, for that you have to save Smiley.
So certain perks that are free as rewards for doing quests and stuff is fine, but challenge perks? No.
Like I said, learn by doing is Elder Scrolls thing, Fallout should not follow that design, even with crappy mini-perks from challenges.

I kind of like the challenge perks. Back when I played 1 and 2 I always wanted some reward for killing 2 million 7 hundred fourty nine radscorpions. But if you don't want them there should be an option to just not get them or something?

hardcoe Mode +1: No challenge perks. (Amongst other things.)

But the melee and unarmed challenge perks are not very easy to get your hands on, you pratically need to play the game since the beginning with those weapons for being able to earn them in a reasonable timeframe that could actually help or contribute to your build (or you need to build an specific build that uses melee and unarmed).
If you wait too much, you'll need to do things like clean Quarry Junction, do Bleed Me Dry or fight Cazadors with those weapons or you will be so advanced in the game they will matter nothing to your character.
Melee challenge also have some neat things, like needing two different type of weapons for gaining all the levels and there aren't too much one hand melee weapons that destroy enemies in a blink.

For example, you can build a character focused in rifles, carbines and pistols, with a secondary combat skill focused in melee or unarmed without needing to pick the Slayer perk, for example.
Or you can create a guns character that uses shotguns for knocking opponents with And Stay Back perk, instead using melee for this.
This allows you to create different characters without needing to "exit" them, like your cowboy using assault carbines or chainsaws.

Others like Camel of the Mojave, stim or chem addiction, applying mods to your weapons and such fall more in your description.