why are beers served as pints in bars but only sold in 12 oz containers?

in the uk and the us, they serve beers as pints (16 fl. Oz/473 mL) at bars but in stores, beers are only sold in 12 fl. Oz/355 mL bottles or cans. why is this? wouldn’t it just be better to sell 16 oz bottles? why are 4 extra fluid ounces added (or subtracted) for no reason?