Because the dirt sheets are reporting that Melina was asshurt that she wasn't in Mania, but Trish was. Then again, said sheets reported that Melina wasn't the omly diva pissed at that.
Adding fuel to the fire is that Morrison was an asshole during the planning of the match and after towards Trish and complaining that Melina wasnt in the match, despite that making no sense. To be fair to Melina, this seems to be more of Morrison being an ass than her.
Adding more to the fire is the reports of Melina being rather polyamourus backstage, most recently from Val Venus. Again to be fair, she is far from the only one, male or female, to be a run around in back with thier pants down.