It makes a lot of sense when you consider what it's meant to measure.
Lakes (and more importantly, reservoirs) are measured in acre-feet. We measure the land in acres. When a reservoir fills up, we can see how much land is covered for every foot the water rises. You create a table for that and you can tell the volume of water based on the depth.
Acre-inches is also commonly used, especially when figuring things like water release from a dam. It's generally not used for things like water in a river, unless an upstream dam is discussing water release with a downstream dam. For water in a river, we do cubic feet per minute.
Yeah, I know, it's not base 10, but we've been using these measurements for a long time and it's not like conversion is terribly hard when necessary - and it's generally not necessary. Ease of conversion is overrated. For example, I do woodworking as a hobby - I have very handy units of feet, inches, and thousandths of an inch (which I rarely use myself, but some woodworkers do). I can convert between inches and feet easily, but I have no need to convert any of my measurements to yards or miles. With metric, I could do these conversions easily, but I'm stuck with a measurement system that gives me no widely-used unit between something a bit less than half an inch and something a bit longer than a yard.
It's the same with most things. How often do you actually need to convert units in daily life? Unless you're an engineer or something similar, you probably don't*.
So you continue to laugh at our measurement system, and we'll continue to laugh at yours.
* obvious exception of cooking inserted here. The metric recipes tend to use measurements of mass rather than volume for many ingredients, mostly because you don't have a very good selection of volume units. Still, anyone that's been cooking for a while knows how many teaspoons are in a tablespoon, and how many tablespoons are in an ounce - and cup->pint->quart->gallon isn't very difficult, either.