Because you can't replace someone who understands you and what is in your life, and you can't replace someone who you understand and who will open up to you and tell you their feelings and their latest gossip. That group tends to be the girls
But it's much easier to replace someone who talks about football and who you have a bit of banter with. That group tends to be the guys
It's sad because I probably make more close friends who are guys and enjoy spending time with guys, I just don't keep in contact with them as well. Perhaps it's because guys are rubbish at keeping in touch.