User blog comment:The Milkman/Mass Effect in Retrospect/@comment-4721065-20130419132524/@comment-3228423-20130420042002

Well there's also the reason that Shepard's the only one that takes the Reaper threat seriously. The squadmates of the first know about the Reapers and are trying to help but keep getting hindered by the Alliance and Council who just denounce Shep's attempts to spur them to action as words of a madman, and Cerberus can't take on the Collectors and their Reaper masters because, due to being an evil terrorist organization, are forced to do their actions behind the scenes so that they wouldn't be noticed.

And yes, I realize that their attempts to go unnoticed by bringing Shepard back from the dead would just get them more noticed but it shouldn't get them as noticed as sending a Cerberus army to do things.