Same as outsourcing security: When you want a team of professional security engineers take care of it. (In that case, you may want to wish they are ethical, not overworked and actually care about your servers…)
Same as outsourcing security: When shit hits the fan, you have somebody else to point your finger at. No inconvenient questions to ask withing your org, potentially having to blame someone you like on a personal level etc.
Worst case, you have to ask the guy who green-lit the outsourcing some inconvenient questions, but if the company you outsourced to is big enough, you can easily take the "nobody ever got fired for buying IBM" escape route.