So I was looking thought the bestiary for creatures and I noticed that alot of feline enemies do not have darkvision when in real life all felines can see in the dark because of the way there eyes work. So why so most felines have darkvision? 

So if you put a cat in windowless room 50 feet underground with no lights on, could it still see? Now, I understand that the monster stat blocks aren't consistent here, (for instance why do tigers have darkvision, but cats, panthers and lions do not? I don't know.) but Darkvision is essentially a fantastic ability that allows a creature to see in complete darkness without any light source whatsoever. Not a common trait for animals to have, even felines. 

This is why in 4th Ed you had the Infrared vision stat, aside from the Dark vision.

It's more like the 3.5 difference between darkvision and lowlight vision; darkvision would work into a completely dark cave or room, wheras lowlight vision would work in twilight but not full darkness. 5E simplified this and, as has been said, Darkvision basically is near-supernatural. 

Quote from LightSpeed >>

So if you put a cat in windowless room 50 feet underground with no lights on, could it still see? Now, I understand that the monster stat blocks aren't consistent here, (for instance why do tigers have darkvision, but cats, panthers and lions do not? I don't know.) but Darkvision is essentially a fantastic ability that allows a creature to see in complete darkness without any light source whatsoever. Not a common trait for animals to have, even felines. 

 darkvision does not let a player or creature see in complete darkness, it lets them see in the dark as if it were DIM light in shades of gray, the same was cats see in the dark in real life, the reason for shades of grey is that when there is less light the eyes can get all the colors coming in so you just get grey, sometimes darkvision can get you into trouble, for instance a player sees a puddle on the ground and goes: hey that's just a puddle, and steps in it and then goes...oh wait that was a grey ooze. also if the cat in the underground windowless room has the tiniest bit of light in there then yes it can see, light does not just vanish when you can't see it, it can bounce around in a dark room for years, that's why we can see the stars in the sky at night, because light that took thousands of years to reach out eyes has.
anyways going on the tangent that the normal CR0 cat should have darkvision still goes. most creatures darkvision do not come from magical means (minus fire genasi who's darkvision is magical and they see in shades of red)

D&D "Darkness" is pretty much the complete lack of light. So even in a room with no light at all, creatures like Dwarves can still see. The amount they can see is the same as a human in dim light. A cat cannot see in complete darkness, it can see in dim light.

cats have high perception, this accounts for their prowess at night. essentially they may have disadvantage in low light but they get a higher roll than other creatures

Felines (more so over large felines) are normally the top of the food chain in the areas they live in, hunting at all hours of the day and night, I seen a jaguar dive into a river, sneak up on a crocodile and snap its neck like a twig. The senses of hearing. Smell and sight are way above canines, ever see the thing cats do were they sit with there mouths open? That's then taking in the air to spell like a snake does, all that coupled with there razor sharp hook shaped claws, bone crushing jaws and speed (most can run upwards of 30 mph) as well as there cunning make them very very dangerous. When I put in felines in my game I run them as cunning predators and my group has fun with it, they went to hunt a dire tiger (witch is a a CR 6 creature and it's the huge size) and it gave them a good run for there money, even gave them cunning action to make them more cat like and my group had fun with it, felling the beast after about 6 rounds, they are happy they didn't run into a ambush of them (a pack of tigers is called a ambush or a streek)

So. Felines have what's called Scotopic vision.

https://www.merriam-webster.com/medical/scotopic vision

Scotopic vision is: vision in dim light with dark-adapted eyes that involves only the retinal rods as light receptors

The term comes from Greek skotos, meaning "darkness", and -opia, meaning "a condition of sight". In the human eye, cone cells are nonfunctional in low visible light. Scotopic vision is produced exclusively through rod cells, which are most sensitive to wavelengths of around 498 nm (green–blue) and are insensitive to wavelengths longer than about 640 nm (red). This condition is called the Purkinje effect.

Scotopic vision occurs at luminance levels of 10 to 10 cd/m. Other species are not universally color blind in low-light conditions. The elephant hawk-moth (Deilephila elpenor) displays advanced color discrimination even in dim starlight.

Mesopic vision occurs in intermediate lighting conditions (luminance level 10 to 10 cd/m) and is effectively a combination of scotopic and photopic vision. This gives inaccurate visual acuity and color discrimination.

In normal light (luminance level 10 to 10 cd/m), the vision of cone cells dominates and is photopic vision. There is good visual acuity (VA) and color discrimination.

In scientific literature, one occasionally encounters the term scotopic lux which corresponds to photopic lux, but uses instead the scotopic visibility weighting function.

This gives you a side by side (top to bottom) comparison of human vision compared to cat/feline vision of same scene

Cats still require light to see in the dark. They just require significantly less light than people.