Why do people not take monkeys as a pet?

A good number of reasons starting with unless you have some primatology background you know nothing in their proper care.
The pet trade, they are removed from the wild and separated from parents before they are ready and that makes for an emotionally unstable pet
few people are even up to the challenge of keeping a monkey that is a 24/7 task. Like a hiper spoiled brat on steroids. you can't make them do something they don't want to do else they get POed, then everything from slinging poop to biting and scratching, even the smaller capuchin has the strength to pull an ear off, or rake your eyes with a tail. Simply put, they can be mean SOBs ina small package,,,can you tolerate that also.
They can't live lifelong in a cage, they need lots of room to free run and will destroy your house if not well monkey proofed. They get loose outside, it is up a tree and they are not coming down until damned good and ready, chase them, they run.
Not all bad, properly bread and separated, they can be very loving and affectionate and social. They may be as smart as you on different perspective.
Can you afford a $2000 vet bill for a simple cold, it goes up from there.
Legalities now mean a strict license, to qualify it means 1000 hours primatology background and an inspection of their keeping facilities.
My focus here is with the capuchin, a small cat size monkey, the typical organ grinder sort.
I can factually say all this as before regulation we had a capuchin, it means no vacations for their life of 20+years, just a trip for the day means a qualified sitter.
Sadly, our little guy (Chico) died prematurely of a lung infection after 8 years. the vet was an hour drive and a refinance of the house for the bill, only to cross the rainbow bridge. Yes, I loved our little pet, it was hard.
As much as I would love the little sihts, no, I would never keep another, not even consider.
They should be left in the wild with their own kind.

They value their property.

because they are super strong and can rip your face off

They belong in the wild and are not suitable as pets because they have complex needs and behaviors. They can also very dangerous.

My friend when I was a kid, had a pet money from when it was little and was very nice to it. In time nature took over and it became very aggressive and it was donated to a zoo.

They bite. They scratch. They fling poop. They are highly susceptible to respiratory infections.

governments of the world tell us we can't

Because they are wild animals and should remain in the wild.

Someone had a monkey as a pet then one day it swiped her face clean off her head.

they feel that the monkey is too closely related and don't like that association

They host transmittable diseases