One suggestion is that a 5-inch mounting could provide coverage comparable to several smaller weapons with a lower weight or volume cost. Another is that an available gun might have suited the immediate design. Both are possibilities raised in the conversation, with no settled explanation of which consideration decided the fit.
Notable Point · 2:14:33-2:14:54
Possible reasons for an escort carrier's single 5-inch mounting
Weight, hull space, and mounting availability are suggested as possible explanations for the single gun.