I feel like this is just the natural losing of friends that everyone goes through in the high school to college, college to "real world". Everyone starts with the best intentions of keeping in touch, but naturally you lose friends and you're left with the friends that you have in your current area and only the best of friends from those periods in your life. They might make an attempt to maintain the relationship, but it's just not enough for you.
I feel like this is just the natural losing of friends that everyone goes through in the high school to college, college to "real world". Everyone starts with the best intentions of keeping in touch, but naturally you lose friends and you're left with the friends that you have in your current area and only the best of friends from those periods in your life. They might make an attempt to maintain the relationship, but it's just not enough for you.