Yeah, Sith lords show no ability to just stare at a random patch of planetary surface and go "I spot rebels there, there, and there." They might well be able to identify rebels from non-rebels at
close range, but it's not like Vader is going to waste his time marching down a long line of random Iraqis trying to single out the rebels.
No, the Imperials would just view this as a routine thing, not requiring Sith attention, and park stormtrooper garrisons in the middle of the place, then slaughter everyone who shot at them and engage in mass reprisals agaisnt the civilian population for shooting at them. Or something along those lines.
Borgholio wrote:they could have been using some technique to deliberately mask their presence from the nearby Sith Lord(s).
Well Yoda was so strong he had to hide on Dagobah near that dark side cave to mask his presence.
He may have initially decided to use the cave to mask his presence, and then spent the intervening 15-20 years working on other, entirely different techniques to hide himself. Which would be useful both as things to teach Luke,
and if Yoda ever had to actually leave Dagobah for any reason.
Or Yoda may have known these techniques already (did Palpatine know Yoda was coming when Yoda attacked him in his quarters during Episode III?), and felt they might be insufficient to stop a galaxy-wide search for him, and thus decided to pick a place where he could be even more secure.
Or maybe the techniques only work when you're awake and concentrating on "nobody here but us chickens, no Jedi at home, go away scrying Sith minds." In which case, again, Yoda would need another place to hide himself where he would be free to go to sleep or concentrate on things other than cloaking himself.
Obi Wan in all honesty wasn't all THAT powerful. There were many Jedi in the order who were stronger than he was. So hiding in a hut in the middle of the desert and not actually using the Force much was probably enough to stay concealed.
True, especially since Vader is unlikely to ever willingly return to Tatooine- there is nothing there for him now, and post-Clone Wars Vader is very much a creature of his own personal neuroses and agonies. So all Obi-Wan should
really have to do is avoid being detected at long range by someone who isn't specifically looking for him there.