IMHO, the mint bungled the Parks quarter series from the start, and that's at least in part why the San Francisco quarters are appearing in circulation.
Many people subscribed to the rolls and bags, hoping to be able to buy complete sets. Philadelphia and Denver coins were sold in both standard 40-coin rolls and 100-coin bags. Correct me if I'm wrong, but I think San Francisco quarters were only sold in 100-coin bags. For collectors trying to buy quantities of sets, that created a weird choice: (1) buy three rolls of the P and D and a bag of S, and spend the extra 20 of the P and D coins, (2) buy 2 rolls of P and D and 1 bag of S and spend the extra 20 of the S coins, or (3) awkwardly keep the mismatched numbers. Then abruptly the mint released the West Point quarters into circulation only, and made the now-incomplete P-D-S sets virtually worthless for those who subscribed.
When I was still doing coin shows pre-pandemic, I can't tell you how many people tried to sell their P-D-S mint subscription accumulations to dealers at the shows. They found that the market was saturated, demand was non-existent, the coins were more nuisance than investment, and blamed the dealers for "trying to steal" their "valuable" coins. It definitely made for less-than-fun moments for the dealers. To avoid the issue, I finally made a sign that read "We do not buy coins minted after 1964." That solved the issue.
It doesn't surprise me that these are ending up in circulation. The Philadelphia and Denver coins must be getting dumped, too, but obviously blend in much more easily.