Why is the <div> option proposed by anyone in the first place?
Well, have you been on, I don't know, TV Tropes? They have those long lists, that are separated into "folders" on a single page. You can click on those "folders" to expand/collapse them, and it's implemented as a <div> with "onclick" property and <ul> inside it (well, used to IIRC; nowadays this <ul> is a child of a sibling <div>).