Not really, except I heard from a good source that Obasanjo encouraged Exxon not to bid and that they would get other Nigerian blocks instead, which they did.
Not a confirmed reasosn but possible.
Others including tghe Sao Tome AG report said it was because Exxon did not want to share a block with ERHC.
However, once they chose not to bid ghat is their decision, same as any other auction. If you chose not to bid, it's only your loss.