No one gave Steph any grief when he first stepped into the league because he was just the fun, baby-faced skinny dude who could really shoot and who might make a few All-Star games. As soon as he started winning MVPs and a title, threatened the status quo, and took away other players' shine, that very much changed. Then, he was the rich, soft, light-skinned, ex-player's kid who never struggled a day in his life (laughable when discussing a 5'6" high school sophomore with serious NBA aspirations), who was attracting casual, predominantly white fans to the league. There was absolutely resentment from the cool kids club, namely LeBron and CP3. Klay caught some of it too for many of the same reasons. Steph didn't truly shake it until 2022.
Obviously, it's much more pronounced in CC's case, but expecting established players to just accept and embrace the outsider who's not "like them" because it makes the entire league more popular isn't a natural human reaction.