I am probably a latecomer to kilt wearing compared to Jock Scot, I have only been wearing them since 1976, but I can tell you none of my kilts have had belt loops either. As Jock says, don't worry about it. Your kilt isn't going to fall down.

I usually wear a kilt without a belt anyway, as I wear a waistcoat, (vest to some), and have had no mishap.