Why do cats always like to bite people's feet?
1. Cats Hunting
Although domesticated cats have been tamed as pets, their carnivorous nature remains unchanged, and it is normal for them to hunt.
Pet cats are usually kept indoors and not taken out, so they rarely encounter prey such as mice or birds. In this case, your feet will be perceived as moving "prey" by them. The movement of your feet stimulates the hunting instincts of kittens that have not yet been trained, which is why they come forward and bite your feet.
Kittens typically begin learning and practicing hunting skills during the weaning process. The peak period for kittens to practice hunting is between 2 and 5 months old, during which their activities mainly involve pouncing and biting, as well as chasing and playing with other kittens.
If you adopted your cat at this stage, it hasn't been trained to hunt yet, and there are no other cats in the house to play and practice with. So, it can only focus its attention on your moving feet. 
2. Game Illusion
A cat biting your foot might just be teasing you, like when you use a cat toy to play with it; it's treating your foot as a toy.
It will be happy when it treats your feet as toys, and over time it will develop a habit of biting your feet. If you don't pay much attention when your cat bites your feet when it's young, it will form this habit, and it is very likely to bite you when it grows up. So once you find your cat biting your feet, you must stop it and not let it become a habit.
3. Wants to get your attention
Cats can get your attention in many ways, such as rubbing against you, following you, or biting your ankle.
Cats that like each other will often groom each other by licking or gently biting each other's fur, so a cat will also do this when it likes you.
