Why is it people (mostly in industrialized societies) always try to rush the baby off the tit?

Why are people (Mostly Western) try to rush the baby off the tit? It seems here in America people are always bringing up why a woman who has a child greater than 18–20 months have not got them on the bottle at least? Kids are not washers with predetermined cycles, just as some will be greatly smarter or athletically inclined than others not all babies will learn to roll over, sit up, pull themselves to their feet, crawl, and walk on cue with all others in baby nation. So why do people think there is some magic cut off date for breastfeeding? Back before we got spoiled with formula, Gerber’s baby food, nice cold refrigerators full of pasteurized vitamin ‘D’ milk, mother’s milk was the only game in town. What did they do back before formula and refrigerators when the kid got to 18 months say “sorry Sparky you can’t have any more from the nipple, try choking down this creamed corn or mashed potatoes”? I think each kid had their own timeline to get off the tit why can’t we adults just be patient to wait it out? What is that harm if it takes a kid 28 or 33 months to move on?