Yes, sometimes it is something from childhood. Sometimes it's a latent or unconscious need to be controlled. Being tied up is about giving up control and having implicit trust in someone....basically trusting them with your life. Being tied up and being humiliated are among what is called fetishes. No one has been able to determine what causes fetishes as there are different causes for different people. So without knowing someones history and background, it would be hard for me to say why that person in particular liked to be tied up or humiliated.
The paraphilia of being sexually aroused by bondage is sometimes technically known as vincilagnia. The most frequent reason cited for bondage fantasies is freedom from inhibition, sexual or otherwise, since they are giving up actual physical power. For some, the pressure or pulling intensifies the orgasm. Some people just like to live dangerously, and see bondage as a dangerous situation.
As a child a person could have strong memories to leather (someones leather jacket, a leather belt), or may have gotten their first arousal from bing tied up during cowboys an indians. Maybe they tried it with one of their sexual partners and it awakened something in them, maybe or maybe not, related to their past.
Some people are so "in control" in their "real" life, and just want to be out of control in their sex life.