Because Sniper King IS the hero this world deserves.
(And yes, I know he's more commonly called "Sogeking" but soge directly translates to sniper and I'm not a weeb who has to say the Japanese word in order to validate my existence, so donm't cry about the fact that I used the English version of the name)
One Piece was and still is my favorite series to date and while in cases like these it can usually be hard to pick a favorite character, especially in one with SO many in it, that has never been a problem for me as Usopp has always, undoubtedly been my favorite character since his intro... wait, did I say Usopp? Sorry, I mst be mistaken! This isn't Usopp, it's Sniper King, his good friend and King of Sniper Isle! Joking aside, Sniper King is the one thing I found in the series that somehow made me love Usopp even more. When I first heard of the character I was intrigued, but the second I saw his theme song I was laughing for months straight! Seriously, I watched the damn thing on loop and sang it constantly and Sniper King went down as one of the quickest cosplays I ever made, as I set out to make his outfit as soon as I saw him... granted it helped that I already had an Usopp one, but that's neither here nor there.
I had actually planned on putting Usopp into the November Countdown, as out of anyone in the crew he's definitely the most fitting of the "sidekick" title, and I was going to put Luffy in the December Countdown instead, but I quickly realized it would be way funnier to just forgo Usopp entirely and place "Sniper King" instead. While this was primarily a joke entry, which is why I'm placing him fairly low despite my love of the character, I do have a pretty earnest reason for putting him in. While Sniper King is essentially Usopp's ideal vision of a super hero with himself in the role, I also put him in because out of anyone in the Straw Hat crew, I always find Usopp to be the most noble. Despite all his lies and cowardice, Usopp always seems to have the most sincere and noble outlook on things. He has a very pure spirit and fights against his own short comings more than anyone in the series and that's why I love him so much. As funny as Sniper King was, the reasoning and events that lead up to it were both epic and heartbreaking, and forever cemented Usopp as a Brave Warrior of the Sea in my heart.
One Piece isn't for everyone and that's fine, and even for One Piece fans I know that opinions of Usopp tend to be on the fence but I say anyone who claims to like the series and not this long nosed coward doesn't truly understand this series. To me, Usopp sums up this series better then even Luffy. He manages to flips the switch from funny to tear jerking quicker then anyone and I don't care if you disagree with me. Usopp is my captain, all the way!