Had they joined the MWC, then they, too, would have had to leave the PAC and therefore split the money with the rest of their ex-PAC mates.
And if they'd invited MWC teams to join this year, then they would have had to split the money with them. It's a substantial amount of cash that OrSt and Wazzu are splitting by being the last two remaining in what is an otherwise defunct conference.
I think, though, that the two schools are overestimating their value to the MWC if they think they can simply drag the MWC along. Those two schools really don't offer much to any conference.