Why do you suppose C. tetani makes tetanospasmin?

Question

What do the bacteria gain from it?

Answer 1

Well, a huge mound of dead meat to feed on (before modern medicine).

Answer 2

Clostridium tetani is an opportunistic organism. It normally live in soil, but will invade animals through wounds. The toxin no doubt helps the bacterium invade animals.

Answer 3

I remember being told that C.tetani make tetanospasmin to discourage microscopic nematodes from eating it in the soil. It just happens to have an effect on mammalian nervous systems too, but I can't find the reference for you.