Aside from the Jedi and Padme's entourage on Tatooine, how many people would even know that Anakin had been a slave, let alone be able to connect the dots to figure out his mom belongs to some junk shop owner in the ass end of nowhere? If anything, moving her around would draw more attention to her. How many times can some Jedi show up at Watto's before someone starts thinking something's up? Or if the Jedi drop off some random lady from Tatooine on a new planet somewhere, that's probably going to raise some questions, most people don't exactly hire the Jedi as a moving service because they want a change of scenery, and since Shmi is kind of a nobody and not some diplomat or something, that would probably make people wonder about why she's getting a Jedi escort.

Any random person Anakin runs into probably assumes he was raised from basically infancy by the order, with no real attachments to his family, just like any other Jedi. Sure, he's not exactly shy about talking about his childhood as a slave, but that's not exactly a common topic of conversation for most people and it mostly tends to come up with someone he's built/building some degree of trust with, so not someone who's going to go try to get leverage on him.

Watto would also probably clue in that something was up that the Jedi were interested enough in Shmi that they came back for her, and ask for like 10x the normal going rate for her, and probably buy a few more slaves to replace her, again, further propping up the slaving industry.