So basically , the point I am trying to make here is that before 1999 modern quarters had an eagle on their obverse side. Apart from the 76 bicentennial quarter there really weren't many variations.
So now there are what? About 60 variations of a quarter?
I strongly suspect that this practice has been contrived out of something other then national "state and federal park" pride.
If every American household is collecting just 1 of each of every commemorative quarter, nickel, etc (I know, one roll of quarters would't last 6 months in the average household, without getting used to pay for something) then literally billions of dollars would be getting removed from circulation to be hoarded.
This is hugely advantageous when calculating money supply, and has thus created a whole new category of "ghost currency"(yeah, I don't think that term existed before about 30 seconds ago either) that really for all monetary "legal tender" purposes, doesn't really exist unless it gets reintroduced into the money supply for face value.
If it is never recirculated for face value, it is a complete 100% profit to its manufacturers, The US Federal reserve. (Ultimately the US treasury itself).
The Mints are really "working" that concept.