>>211395891 (OP)Anakin was told that both Padme and her child died. He didn't know that there were twins, and that they lived. This is why he gets all excited when he finds out Luke isn't the only option for a sith apprentice (because he has "a sisteeeerrrrrr").
Skywalker is a (reasonably) common name among humans on Tattoine. Vader hated the planet andnhad no reason to go back. The Hutts ruled most of it and the Empire barely had a presence.
Was it the best idea ever? No. But it wasn't terrible.