liter is a unit of volume, not weight or mass. If I said "half a liter of cherry tomatoes" or "half a liter of strawberries", you'd have a good idea of how many I was talking about, without knowing the weight. The US only peripherally involves itself with metric measurements, but due to the fact that sodas come in 2 liter bottles, I know about how much a liter is I can easily and quickly visualize a half-liter of strawberries in a way that I can't with a statement like "8 ounces of strawberries". You could show me 8 ounces of strawberries, but that doesn't mean that I could use that knowledge to easily and quickly figure out how many kiwis make up 8 ounces. But I bet I could estimate a half-liter of kiwis pretty easily.
bushels, pints, etc, are simply other units of volume that you might not be familiar with. I can show you a picture of a bushel, and I'd bet that you could instantly mentally apply that picture to estimate how many strawberries, cherries, or squash might fight in it. You can't really do the same for, say, a kilogram or a pound. It's not as convenient as quick estimator.
It's easy to look at things and quickly estimate how much space they take up (volume). It's not as easy to look at things and know how much they weigh.