I dont know why, but I can tell you yiur reaction is perfectly normal. for some reason or another you subconsious was just not ready to deal with it until later or you were stll in a state of shock.
dont abuse yourself more because you didnt react the way you think you should of.

i was abducted and raped 3 times,(not seperate insidences) I remember wondering why I did not feel angry, I did not feel anything. I told myself someting was wrong with me because I should fell something. I should feel hate, anger, revenge. I put it behind me and went on until 20 years later, I was walking out of school and it had turned dark and i froze, scared to death to walk out the door. I dropped the class and took no more night classes.
Still not dealing, just wanted you to know its a normal reaction.

hope this helps you understand yours.

i think it is maybe a form of self protection or preservation

I understand. It took me years to finally realize what happened to me. I too think that it's some kind of defense for ourselves. The important thing for you is that you now do realize it and hopefully can take the next steps into recovery. I hope all works out for you.