This is because of the specific function of every part of the body.
Fingers, the part of the hand that helps us discover and things and their characteristics, had more receptors than our back, for example.
This is because our back needs to feel things like cold or heat, but not necessarily recognize things or recapitulate information about it.
This helps us to survive because if you don't know something, you may touch it and if it feels too hot, or itch, or have some bad reaction you will move away, preventing of being hurt.
