Explain why cytotoxic T cells are not affective against bacteria.

Because cytotoxic T cells are activated with antigens.

Explanation:

Cytotoxic T cells are a type of white blood cell that expresses T-cell receptors that can recognize specific antigens to then be activated by them to neutralize an infected cell, antigens are structures that can stimulate an immune response, they are presented by the cells so T cells can identify them.

So, based on the previous information, cytotoxic T cells can't recognize or attack bacterias if their T cell receptors don't have an antigen presented by another cell to bind.

I hope this information clarifies your doubts!