Why submarines keep weapons inside the pressure hull

Why not replace torpedo tubes with external weapon capsules?

Internal tubes support reloads and larger magazines, while external capsules add drag, noise, and additional structural penetrations or weak points.

An external capsule can simplify one launch but makes repeated engagements and weapon handling harder. It also disrupts the smooth hull form a submarine relies on for low noise and introduces more fittings whose structure must survive pressure and flow.