Because that is our great hope Dan. And because it is a kindness. Much as some people seem to want the job, thankfully God does not task us with the hard job of deciding who actually gets the door locked on them. We aren't qualified.
Nor is there anything humble about putting forth notions about eternity that oppose what Jesus repeatedly taught (Matthew 7:21-27; John 14:6; etc. ad inf.).
Further, see my post just before this one.
If it is improper for us to pronounce someone whose life showed no trace of living faith in Jesus Christ to be certainly damned (as I believe it is), it is equally improper to pronounce such a person saved.