Just Curious...proofs

I had thought it was because they polished the dies differently but take my theory with a grain of salt

The frosted areas on modern proofs is courtesy of vapor blasting the relief areas before striking. On the older proofs, most of the design elements have a mirror effect. Only the earliest strikes from a new die or repolished die would have frosty design elements, as more coins were struck this feature would wear away on the die. Consequently, proofs with cameos are relatively rare to scarce from 1950 to about the mid-1990's on some denominations. Today almost all proofs issued by the US Mint are CAM or DCAM.

Cameo and ultra cameo proofs on coins prior to 1965 were artifacts, not the intended look of the coins. They were intended to be fully brilliant coins but they did not have a good way to polish the devices other than to let the first few strikes do the job. The look became popular among collectors (the same look had appeared on small run proofs of the late 1800s for the same reason) so the mint spent the effort to find a way to produce cameo coins in large runs. In 2003 they experimented with a laser instead of sandblasting the die before hardening and the look achieved was very good (2004 National Wildlife Refuges Medals). Unfortunately, it was expensive, and to reduce costs the mint lowered the resolution of the laser "etch" which has resulted in significant loss of detail in the devices. It does however cause very high contrast between fields and devices. The traditional and now the vapor sandblasting is still in use on uncirculated coins, where contrast is not a factor but detail is. I wish the mint would choose detail over contrast for the proofs as well but they don't seem interested in doing do.

OR the Mint hired a Chrome Plating service for autos to redo their Proofs.