MU will probably be regretting their move in five years too...
The difference of course is what they're leaving. WVU is already in a geographically far flung conference that is on the verge of collapsing. It also pays very little.
Missouri is in a conference whose main source of instability is Missouri themselves. That conference is geographically aligned in the Plains states and it has a very large and lucrative TV contract.
The Big East is going down the tubes. West Virginia has to leave to stay in a relevant league. Missouri is already in a relevant league.