A lot of girls make guys wait because a lot of guys have a habit of pretending to be romantically interested in a girl, then as soon as she sleeps with them they're not interested any more. They like the thrill of the chase and string you along making you think they want a relationship until they get what they want.
It's happened to me and a lot of my friends. I went on four dates with a guy over a period of a month, we slept together then I never heard from him again, found out all the time we knew each other he'd been sleeping with other girls. I don't blame people for waiting, maybe 4 or 5 months is a bit long but it's better than jumping into bed with guys straight away, because 9 times out 10 they're not romantically interested in you at all and just want sex. Not all guys are like that, but unfortunately a lot are.