Well, for one, it prevents this
And there are many reasons. The biggest reason to do it is the utter lack of reasons NOT to do it. It can’t hurt but it can sure help. I’ve shorted things out by mistake a few times and fused charge ports are definitely good. It’s one more layer of safety net between “okay” and “fire”. Especially if you leave your board to charge unattended — and let’s be honest here, literally nobody stares at their board for 3 hours while it charges — then it’s one more layer of reassurance.
Plus, we are human and you never know what can happen.
You know, legend has it that one forum member got home once after drinking a couple brews and the girlfriend figure was asking 50 questions while the dog was in lick-your-face mode and while trying to plug in the skate accidentally stuck the door key in the charge hole, because dumb. Fuses help that kind of thing too.