I honestly have no idea. The massacre is barely brought up again in RotS. I think that Palpatine is the only one who mentions it and he only does so once. Nobody else - Anakin, Padmé, Yoda - ever brings it up again.

Maybe George Lucas thought that it was just some foreshadowing for what was to come? Well, I hate to break it to you, Mr. Lucas, but slaughtering an entire tribe isn’t a stepping stone on the way to the Dark Side; it’s a big, flashing neon sign of having *already* become evil.