> You don't need stickers for grip (and fact they're not ideal for that anyway)
You don't need to eat chocolate cake for sustenance (and in fact it's not ideal for that anyway).
It's a minor practical benefit to having a sticker collection on there, which is different to covers, or tape, or other things.
There probably aren't millions of discreet reasons, but there are millions of people with their own reasons, even if they largely overlap, the rationale will be slightly different.