What if... Sabo couldn't be there ?I am not saying that sabo doesn't deserve it but
But where was his "brother" when ace was captured and was about to be executed?? He didn't risk his life for ace while luffy went head on against his own grandfather and all the admirals to save ace while sabo didn't even show up.....just saying when ace needed help "the brother he had been longer" for didn't even show up while luffy almost died for him
Again not saying sabo doesn't deserve it....
Good enough reason ?
It's not like they will send the entire world a notice so that they can prepare all kinds of stuff. They were already crapping their paints when Whitebeard took down his 12 ship Navy detail. They said his execution will be in one week, and Luffy needed that entire week to get from Impel Down to Marineford, using the Gates of justice twice and he arrived half way the battle. So imagine Sabo being any where else in the world. He would've never made it in time.
Case closed, unless Oda will come up with something better.