User blog comment:MightySeddieWarrior/Let Sam Sing!!! (Petition! Please Sign!)/@comment-2032682-20110715055902

Sam doesn't sing because Jen signed with a record label not affiliated with Nickelodeon/Viacom, because she didn't want to have to do the pop singing that Victoria/Miranda do. Legally Nick/Dan probably aren't allowed to have her sing, and it's likely the people who work above Nick/Dan would stop her from singing because she's not signed to them.

That's just the way it is. Jen decided to pursue her music career outside Nick/Viacom, and her not singing is the result.