You really expected a former Jedi would be quick to believe that you're telling her the truth? Or to agree to become what, another Sith with you? When you've done nothing to earn her trust or done anything to prove you're not lying.

[ Maul was powerful and cunning enough to manipulate the Mandalorians, but his attempt at dealing with Ahsoka? Of course she'd see through that. Ahsoka was a smart one. ]