Marines are different zkkturd, stop bringing irrelevant shit. Those underlings don't have ambition to be strongest, that's why. Marines might have the ambition to be the strongest marine, but underling pirates like Rayleigh, EoS Zolo, Oden etc won't ever have the ambition to be strongest pirate because they are underling to another pirate because they are weaker than that pirate dumbass, if you don't understand the difference then your brain is too slow nothing I can do.
Strongest marines ambition = Admirals
Strongest pirates ambition = Strongest Pirate Bosses
Pirate underlings can't be inside of the strongest pirates group, its that simple, once they quit being a pirate underling they can have ambition to be strongest pirate.