State some then >_>
Upbringing
Current life matters
Personality
Self esteem
Intelligence
Mental disorders/lack there of
Level of maturity
Appearance
The list goes on and on of variables that play into. For some people, it isn't as simple as going "HEY. WE'RE FRIENDS NOW." to someone. For others, it is. Circumstances and situations change, people are different.
But once again, there are a good number of people who get so caught up in themselves and the quarrels they perceive themselves to have, that people sort of scatter away.