Brake shoes wear unevenly because the shoe table, (the metal part) drags on the backing plate.
To prevent this wear, clean the backing plate shoe slides. Sometimes you have to use a low speed grinder to even out the surface and fill the void with a welder, or replace the backing plate. Any grooves or divots in the backing plate will cause the brake shoe to stick in the rough spot. Use a good quality lithium based, waterproof lubricant on the the slide. When the shoes are assembled on the backing plate they should slide forward and backward with minor hand pressure. Don't forget that worn hardware will cause the shoes to drag on the drum too, and that can cause excessive wear / uneven wear. If in doubt...replace the spring kits.
Most machine shops can turn the drums to be sure they are not out of round, always a good idea!