The judge rarely matches the full request from the prosecution anyways, and normally it can also be lowered on appeals, that's not the point.
The point is whether the request was excessive in light of federal sentencing guidelines, which the prosecutors themselves don't have control over. I actually do not like these cookie cut guidelines, and it should be an integral part of criminal reform, IMO.
But, that's what prosecutors have to work with.

why does this matter? My opinion is as good as anybody else's opinion.