The pelvic floor muscle has a lot to answer for with incontinence but it's only part of the large system that makes up the core. In fact, many people think doing Kegels all day will help with incontinence by strengthening the pelvic floor muscle. In some circumstances, perhaps. But for many, Kegels in isolation and strengthening of the muscle aren’t ideal.
The pelvic floor muscle needs to lengthen and contract, just like any other muscle. It needs to hold tension and be able to relax. It needs to carry load (our Pelvic organs!) and be flexible to allow the exit of things, like urine, out of our bodies.
It needs balance. Just like other muscles in the body, if there are imbalances from over strengthening or weakness from undertraining, we run into issues. This is how the pelvic floor (as well as the rest of the core muscles) can present its’ issues; with incontinence, pelvic pain, prolapse, body pains (knees, back, hips, shoulders, feet!).