The phenomenon of decreasing package sizes definitely isn't limited to ammo alone. Pay attention to your groceries for a while:
1) A box of my favorite macaroni is now 6oz. It started at 7.25oz, then went to 7oz, and is now at 6oz
2) Orange juice used to be commonly sold in half gallon containers. Now you get something like 59oz, down from 64oz.
3) Look at your favorite cereal. This is a real common example of shrinking product sizes.
4) Pasta, too. I used to buy a 1lb package of pasta. Now they're 10.2758oz, or 12 oz, or 13.1243 oz, or some other number.
Reality is, consumers seem to demand the same prices that they've paid for things for many years. Companies are providing those "prices" by reducing product size. You're paying more, and getting less, but it isn't obvious unless you pay attention.
Nevertheless, I always considered a "brick of .22lr ammo" to be around 500 rounds. The shrink started years ago, and I've seen a lot of bulk packs running as low as 325 rounds these days.