The factories do not pay a lot of attention to the internal dimensions of the brake drums.
When the brakes adjusted until they are just free from contact, pull on the brake lever as if you are making a major stop. Take a look at the brake arm in relation to the brake input shaft. Imagine if the brake input shaft is at the very top of the backing plate (or at 0 degrees on a circle). If when the brakes are fully applied the brake arm is at or approaching 90 degrees, then you can squeeze the brake lever all day and you will get no additional pressure on the shoes to the drum.
If there is still meat on the shoes, make some U shaped shims out of a tin can (not aluminum) to go over the ends of the brake shoes where the end of the shoes contact the brake cam. This should re-establish your brake torque-ability.