Why does the Bt toxin not kill the bacterium that produces it but kills the insect that ingests it?

Bt toxin is produced by the bacterium, Bacillus thuringiensis. Some strains of Bacillus thuringiensis are capable of producing proteins that kill certain insects by forming protein crystals that contain a toxic insecticidal protein. The Bt toxin protein can exist as an inactive toxins but once it is ingested by an insect, it is converted into an active form of toxin due to the alkaline pH of the gut of the insect that solubilises the crystals. This activated toxin then binds to the midgut's epithelial cells and creates pores which causes swelling of the cell and lysis leading to the death of the insect but not of the bacterium that produces it since it remains in the inactive form in the bacterium.