Leaving to one side all debate over the stadia within Manchester and whether the resident clubs/ stadium owners would want this event on their pitches.
Manchester for the fans of Wigan, Wire, Saints, Salford, Crusaders, Cas, Wakey, Bradford, Leeds, Huddersfield is within a very easily commutable distance meaning that they would almost all drive to their game on the day and go back home after it. Even those that watched all games on any given day would not need to stay over. At most the Hull, Hull KR, Quins and Catalans fans would have to stay over for the weekend and I think that the Hull clubs fans would be equally likely not to stay over in Manchester and to attend their own clubs' games and go home.
As a consequence the potential for income to local businesses would be much poorer (they would make the same if not more when City or United are at home than they would from this event) in Manchester than it would be for those in cities where most fans had to travel a long distance to get to. There is less incentive for Manchester's tourist board therefore to put in a large bid to stage the event. So even if Manchester have submitted a bid to host it (Richard Lewis said on Thursday on BBC Radio Manchester that a number of cities are interested but didn't name any) their bid is unlikely to be equal to the amount bid by cities such as Edinburgh, Cardiff, Newcastle, Dublin, London (used as examples due to posters suggesting them) that would stand to make much more from tourism while hosting this weekend.
A Manchester bid would be unlikely to be accepted therefore over other bidding cities even if one was made as it would mean less profit for the RFL so less value in holding the event.