The market value of a coin depends majorly on supply and demand ratios. Rarer coins in good condition have a better demand. Rarity is based on low-mintage. For example, only 5,008 1933-D Oregon half dollars were struck out of which only 3,000 exist today. Pricing would increase if the number of collectors seeking them also increases.
When it comes to Liberty Head quarter eagle, collectors are interested in better dates with CAC stickers. Experts believe that there would be just 50 Dahlonega quarter eagle issues in EF with CAC approval. If half of these coins are a part of tightly-held collections, there would just be 25 Dahlonega quarter eagles in EF with CAC stickers. Now if three new collectors bring these coins out in the market, there would be a big impact on pricing.
It was difficult to sell an 1872 quarter eagle graded MS62 by PCGS with a CAC sticker a few years back, even though it is scarce. However, there is a lot of demand for these coins, due to which, many new collectors are bringing them out in the market.
In short, if a coin has limited supply, even a small increase in demand has a big impact. This is happening with Liberty Head quarter eagles in good condition, and the trend will continue for some more time.