I think sometimes people befriend those that make them feel like they're worthy of their attention. We date bad people because we feel like an exception to their sh-tty behavior, we befriend similar people because they make us almost feel apart of the ingroup.

In my own experience, I've noticed that you're right, that people do have a tendency to flock towards those who can offer them not good friendship and unconditional support but to those who they subconsciously put forth such effort to prove themselves to until they're able to just feel almost 'accepted', likely not seeing how toxic their behavior actually is.

I say this because I once had an Amelia in my life with almost an identical scenario. In my case, my Amelia we can call Valentine (or Val for short), who was stranded by a girl we'll call Elena. Once Elena and Val weren't as close, it was convenient that Val and I became super close, along with the addition of another friend of ours, who we can call Alison.

Fast forward a couple years and Alison has a lot of popularity and is more social and I move away to a different state. Val calls me and messages me quite frequently about how alone she feels, how she is being neglected friendship wise by Alison, and how she misses me. I return to our state of residence and she doesn't have that same welcoming vibe she did at one point, and as we spend the night talking to catch up, her foul words against Alison impact my views on her. I soon notice Alison pushes me away as well and go on a rant to Val about how I agreed with what she way saying, that Alison wasn't a good person. But as soon as Val hears this, she uses it to become closer to Alison and cut me (a loyal friend of a couple years to her) out of the picture. Shortly after, she uses this upper hand and befriends Elena once again as well, as if neither of these two girls had hurt her before.

Sound familiar?

I think that's just how life is. I think people tend to gravitate towards those who treat them less than great just because the short term gain they get from these people is nice.

I'm sure I can go on (because trust me, my friendship experience has been less than stellar in the sense that I've been betrayed far too many times despite only ever trying to be there for others) but I think my point has been made, mostly saying that until people can recognize what is good for them and see their own lack of better judgement they'll just continue to surround themselves with others only looking our for themselves.

Even though this really isn't an answer to the question, it's kinda just food for though just to try to make sense of it