I guess people just do it for shit and giggles, ngl it feels good to see your fav character shine so much. I am really really happy for Sanji.
But if you check out what sane Sanji fans post, you can notice that some of us admit that Sanji upscale = Zoro upscale, and many people are simply excited for Sanji w/o trashtalking.
Me personally, I like both Sanji and Zoro as OP characters, to the point that some Sanji fans call me a rat (guess friendship with
@Mr. Reloaded doesn't make me trustworthy lol plus I am not delulu to challenge Oda's Luffy>Zoro>Sanji dynamics, even if the difference is small, it is still there). But I don't like toxic Zoro fans who are Sanji haters and constantly bash my favorite character, so I kinda feel vindicated that they are proven wrong? I usually don't care about power scaling, but these last few chapters were really enjoyable and finally put an end to numerous threads "Sanji is #10 in SHP strength-wise" "Sanji is forever CoC-less, all hail Zoro the most OP OP character" when it's obvious that Sanji and Zoro are really really close power-wise, and if one gets a power up, then another one will as well.
TL;DR we Sanji fans are happy. Feeling vindicated after years of abuse by certain toxic fans is a bonus and some of us cannot still glazing Sanji and talk back to those toxic fans.