Why are individual quarts of oil SO expensive compared to 5 quart jugs? I understand bulk is cheaper, but come on. Example: Valvoline SynPower at Wal-Mart 5 quart - $22.67. = $4.53 per quart 1 quart - $7.74. = $7.74 per quart The singles cost about ~71% more per quart! Why the insane difference?