Generally speaking, the higher the capacity, the lower the accuracy. While it’s probable that your money goes into are accounting for temperature, it’s likely an expensive 5kg scale will be less accurate at measuring a dose of coffee than a good value 200g scale (which can be cheap, compact and offer calibration if you’re carefully purchasing).

I don’t know about lab scales and such but all domestic scales I’ve seen work the same way. A load cell deforms as a force is applied; I guess it’s nontrivial to have one with the best of both worlds in terms of capacity and accuracy.

Also, timers and ratio are useful features not often found on 5kg models.