That's the thing about offers. If the TIGS make one at say 10 bucks they are saying that they think 10 bucks is fair. If someone tops it at 15 bucks and the TIGs say they won't sell they have just told the market they believe the shares are worth more than 15. This leaves them in a ackward position and no one will believe anything they say as they will always been seen as too self serving. Remember it is about fair market value. I believe the only thing keeping the TIGS at bay is the chance of a better offer. If they thought no other offer would be forth coming then they would make a bid.
As well if they made an offer this would then allow MPV to look for a better deal and to get that they would take all available data to possible suiters.