Warner is at least a decade older than Leinart. It's not surprising to me they didn't hit it off, especially considering Leinart's lifestyle choices when he first got here. It would surprise me if Warner didn't try hard to make a connection, but I'm guessing Leinart never wanted Warner as a mentor because that comes with more implications than just football.
On the flip side, Warner seems to have taken Leinart's side in the interim, noting Leinart didn't get a lot of snaps in the preseason. I think it shows Warner was at least somewhat emotionally invested in Leinart's success.