Because former is Oda putting all #2 in same cover explicitly to show them as #2 of their crews.
The latter is your desperate interpretation of Sanji getting to do some cool thing that Zoro does almost if not literally every other time for 1000+ chapters.
@KiriNigiri showed, Zoro also has similar panels with literal captains of Killer and Bepo. So what do we make of that now?
Hell, have some more:
I guess Sanji is not a part of monster trio anymore because Jinbe got to do all these parallels with Luffy and Zoro all while having #3 highest bounty?
Yeah, no, it doesn't matter.
Shove hypocrisy back in the bag, Chrono-kun. Sanji doing what Zoro does for once in his lifetime, just like Jinbe above in regards to Sanji, and you start pretending like it matters over other 1k chapters and explicit cover page lol.