['It didn't', is what Near could say. It hadn't lasted very long, with Mello disappearing before either of them could get any decent benefits out of it. Near had suffered the negative effects of the separation with none of the positive ones from having been a part of it in the first place.

But it could have benefitted them greatly, had things gone differently. Near fully believes this.]

You needed a bond with a monster. Double witch bonds are unstable at best.

[And his bond with L was hardly stable even without it being between two witches.]

I needed a bond in general. That was the most immediate reason.

[Who else could Mello have bonded with at the time? He wouldn't have been able to delay too long with his choice. Near was the only obvious answer.]

Despite our rivalry, we're very compatible. We also have a similar knowledge base. Otherwise you'll be choosing from among the other Mirrorbound here.