Just guessing, but ...
Etrian Odyssey is supposed to be an old-school type very difficult dungeon crawler. Hardcore game.
Rune Factory/Harvest Moon are like those capsule games where you have to collect a bunch of rare hard-to-find stuff to get special items mixed with Animal Crossing "live a life each day" gameplay. People play these games for years, so it follows that those who like it really like it.
I think it also helps, that Etrian Odyssey, Harvest Moon and Rune Factory are established series with a history of western releases. It's easier to get excited when you know you'll be able to play the next game in the series.