It seems to me, being "popular" is more an attained status rather than any kind of quality. What I mean is, the kids who went along with the group gave the group an opportunity to evaluate the newcomer - and gave the newcomer a chance to build some level of likeability, trust, respect.

One may be all of those things, but without giving the group an opportunity to discover that for themselves, they aren't going to listen to your suggestions. Or one may start by going along with the group, but be abrasive and obnoxious, and no matter how much time they spent with the group, they won't be popular.