What you are noticing is an appreciable amount of circulation wear on the on the 1890 relative to the 21
Wear hits the edges hardest. Take a look at some slick Barber dimes sometime -- you can probably get 70 of them stacked into a tube that's supposed to hold 50.
Just look at the rim and the pattern just on the inside of the rim of the 1921. Then compare it to the more worn down rim of the 1890 coin.
The rim is, by definition, the thickest part of the coin, so they can stack. Entire designs have been reworked because they did not stack well. Conversely, the rim is relatively narrow, so the weight of metal lost even for all the visual difference is fairly minor.
