I use Amps and hours in my everyday life much more often than Joules. The manufacturers used those units (which are both SI units) because they are the most useful in this case. If you know how many amps you are using you know how long your battery will last. If they gave the joules remaining they would need to give you a Joules/time reading to get the same information. To get that value they would have to measure how many Amps were being used so why bother converting it?

Maybe you should learn a bit more about Amperage instead of expecting everyone else to learn about Joules.