I think the premiums go higher as you go up in grade or are already in condition rarity for a particular type. To the extent that the CAC sticker also creates an additional "condition rarity" it can also be a self-fulfilling circular thing. Also, JA tends to be "tougher" on certain coins -- gold coins in general, Saints in particular -- than rare types where there aren't hundreds or thousands of coins to choose from.
Far too many CAC saints appear to be technical grade "C" with a luster bump. His opinion doesn't really help me find coins I like. Several years ago, I sent him some of my saints & he didn't like them either. I think "tougher" is relative.
Picky is probably a better word but yea its hard to get stickers on gold coins especially high end ones. CAC isn't any easier on rare types either theres plenty of those with minuscule sticker rates
Plus, it's a big coin with big fields relative to many other coins aside from Morgans. A Mercury Dime has less chance of showing marks than a Saint or Morgan.
The problem with most Saints is the friction. Gold is softer too which makes it more prone to things happening with a heavy coin. A lot of gold in general has been processed in the past too