Why do guys always try to hide girls (who are their friends) from their guy friends?

[Guy]

So several of my guy friends know many girls outside of my school, so I was hoping they would introduce me to them (my friends totally is not dating them at all either). However, every time I try to get them to organize some hangout with those girls, my friend always bails on the idea (makes excuses and never organizes the event like he says he would). Another one of my friends clearly knows so many girls at different schools, he snapchats and facebooks them all the time during class, yet when asked if he knows any girl outside of school, he quickly responds "No".
I really just want to know why guys do this. It's not like they are dating these girls, and like each one of my friends knows like 10 each, so if they were thinking of dating, there are others they could help me meet. Is it because most guys think it is some kind of trophy or competition, so they sabotage the other players? Note, I am a guy too, but if I had friends who were in the same boat, I would totally introduce them to other people.
Thanks for your thoughts and opinions

[Toshiro]

Because your friends are just pretending. They dont really know those girls.

[Sandy]

Those girls are part of your friend's harem, and they don't want another guy encroaching on their turf. Find your own girls if your friends are too insecure to introduce you.