u order, suddenly seller told u that item not available. it is out of stock

now heres the issue
should seller cancel the order
or
buyer cancel the order

actually the seller can cancel their order by saying out of stock
but some seller insists that buyer cancel the order which i find rather fishy. they dont want to cancel the order even though it is their fault

is there any reason why seller dont want to cancel order?

so far i know its on seller discreetion. if seller dont approve. no refund