Sardines are rarely discounted for more than a $1, at least for the brands I like, King Oscar and John West. I eat canned tuna 2-3 times a week but like to switch up some time.
I thought sardine is supposed to be cheaper than tuna, so why is canned tuna 50% off every other week, but canned sardines aren't.
Because price is not determined from cost. Price is determined from demand.