I left this reason out of my last reply. IMO, this is the second primary reason. Except for the money, 20th century and later US sets are easy to complete, excluding Saints and Indian $10 gold which have a low number of rare date/MM.
I learned the hard way to put quality first. When i was younger i would hurry to fill holes in the albums, but i always had to upgrade because i wasn't happy with some of the coins. Even worse, when i sold some of the sets i put together, the buyers attention was focused on the lesser coins in the set. Today, I'd rather have holes to fill than coins i regret buying.