>>673670leaves is at least part of a fairly standard pattern.
Leaf > leaves, knife > knives, wife > wives, shelf > shelves. Even in places where we dropped the f-to-vs form it doesn't actually "sound" wrong if you say for example "rooves" instead of "roofs."
>>673814The other thing is that by virtue of how irregular forms develop, irregular words tend to be among the most common words so you often learn them before you really have the ability to understand how weird they are.
A lot of the time, irregular forms are cases where it USED to be the regular form, the regular form shifted to a new regular form, but the most commonly used words have people just continue saying them exactly the same, so they keep the old regular, now irregular form.
