>>357000611. People are usually unsure about paying for spin-offs. Games outside of main series are made by different people and have different formulas.
2. Quite a large number of people tend to emulate games (for different reasons - poverty, wanting some kind of "demo" or plain thievery) but Ranger was/is borderline impossible to play on Desmume.
Third reason:
3. Gameplay is extremely repetitive. On top of that, it tires your hands and wears down your NDS. It's not as easy to pick up and play as many other titles in the franchise.
That being said... Guardian Signs > Original > Shadows of Almia.