Also, Tattoine is Hutt space. The Republic doesn't exist out there and even when the Empire eventually moves in, they've got their hands full with the local thugs, smugglers and other undesirables that inhabit population centres like Mos Eisley.

I'm sure that moisture farmers who live out in the sticks and crazy old hermits who live in sand people territory barely show up as a blip on the local stormtrooper garrion's radar (awesome fan parody videos aside).