Several reasons you don't want to do that. The first is that the FO probably hasn't quite given up on this season so sending a guy with a 7.50+ ERA for the last month is telling fans they don't care about the season. Secondly, Romero could use some confidence. Getting beat up regularly in the majors isn't good for anyone. It creates self-doubt and forces him to overpitch. Let him relax. He'll be up again. And, as others have noted, he'll be on an innings limit this year so a bit of rest right now won't hurt him. Lastly, the Twins have other guys in AAA or on assignments that also deserve chances to pitch in the majors. Mejia made 21 starts for the a playoff team last year and is posting a sub 3.00 era in AAA right now (and has been even hotter over the last month). Keeping him in the minors while someone else is struggling as bad as Romero is right now probably sends a worse message to AAA ballplayers.