The penis isn't a bicep. With a biceps workout, the goal is to forcibly break down muscle tissue and toughen the tendons and ligaments through contractions against resistance. The resulting cellular damage requires several days' rest for recuperation and overcompensation. You can also stretch the fascia of the biceps to allow it to expand further, and this is where there's some similarity with PE. Fascial stretching doesn't cause the extent of cellular damage that muscle tissue breakdown causes, so you don't need nearly as much rest. There is some ligament toughening in PE workouts from stamina work but the volume is (or should be) as such that you don't require several days' recuperation, as overdoing stamina work can be quite panful and even lead to temporary ED. Many people like to compare PE to a bodybuilding workout, but it's actually more like yoga or a gymnastics workout for flexibility in the way it affects the penile tissues.