Why are some snakes so extremely venomous?

Question

Some snakes are so venomous they would be able to kill many people but generally there diet is smaller animals rodents etc.

Doesn't add up somehow.

Answer 1

Its so they can protect themselves and their territory from invaders and enemies

Answer 2

a snake is not poisonous just because its feeds on smaller animals...it can be that it has to fend itself from bigger animals, and protect themselves... so over a period of time, the snakes got evolved and so did their poison toxicity... and we can still see that