@HSHorror
I think this is generally true.
Also people who seem nice to their friends but not so nice to siblings.
A lot of people try to.be friends with minor celebrities. Or those with big houses /cars.
They get upset if their kid is left out but then frequently let their kid leave others out
A lot of people are friends when they serve a purpose like nct groups or birth groups then drop out as they move on.
Bear in mind the popular people know they are popukar and can make friends easily so drop them easily
But unpick this a bit
why is it significant that someone isn't 'nice' to their siblings? Many people post about unpleasant families on here there's no obligation to 'be nice' to family members who may behave badly to you just because you share parents -- it doesn't necessarily mean that your relationship with your sibling is somehow more the 'real you' than your relationship with friends you chose. Many people are far closer to their friends than their siblings.
I have genuinely never encountered anyone who befriended someone because of their house or car, but our fame-obsessed society's fucked-up attitude to minor celebrity makes it logical for people to attempt to befriend someone they have been taught to consider more important or successful then themselves. (You see it on here all the time on 'What celebrities are really nice?' threads, where people are thrilled to have touched the hand of/shared a lift with some soap actor/TV presenter, and have cherished the details of the encounter for years.)
I think children should be encouraged to choose their friends carefully and according to their behaviour -- DS and his friends (all 8 at the time) gave the new boy in their class a series of chances, inviting him to the park with them after school etc until his violence made them drop him like a stone. I'm sure his mother thinks he's being unfairly excluded, but frankly, no child needs to give still more chances to someone who thinks repeatedly kicking them in the stomach is OK.
A lot of friendships are for a season rather than eternal I don't think there's anything wrong with moving on from NCT groups and the like. You might keep individual friends you particularly gelled with, but those groups are mostly temporary in nature, for support while you're all at the same (challenging) life stage. People move away etc. It's pretty rare for them to bond for life that doesn't make them any less valuable while they do last.
I wouldn't describe myself as 'popular' but I have no problems making friends, partly because I've moved around the world a lot and am used to going out and making new friends in places where I know no one -- I'm a bit puzzled by your logic that knowing you can always make new friends makes you a fickle friend. The flip side would be that only people who are virtual social outcasts are good, faithful, longterm friends, because they know they won't be able to make any other friends, which is a bit depressing, to put it mildly...