The impression I got of Sand people in the original was scary territorial nomads who are best avoided. The novel pretty much says this in the photo insert. The snipers on the pod race course are consistent with that. It's interesting we never saw them (or at least heard them) in Jedi. Jabba's palace isn't exactly in a nice neighborhood!
If you follow the old school of thought about how Star Wars is a "space western", the sand people fill the same plot function as hostile indian tribes would. This would also make the Jawas the friendly tribes settlers could do business with.
Kidnapping Anakin's mom, and basically torturing her seems needlessly sadistic, even for them. Unless it's yet another component of Palpy's decades long plan of improbable events helping his rise to power...