I believe it is due to the fact that those are mentioned in folklore and we don't know if that is fact or fiction. Can't say I have ever had a testimony of someone having experience with them either whether imagined or real.
I believe Muslims are not supposed to say trinity. Of course that is because they don't understand it and for that matter many Christians as well but the Biblical fact is a Trinity.
I believe Abraham's son was a gift from God. Sometimes we get the idea that we own our children when the truth is they are only given to us for short time. I have mine back because they live with me.
I believe I am glad. I had a friend recommend a book series and I really enjoyed it. I think a lot of people have: Fire and Ice series made into the tv series Game of Thrones.
I believe it is like the Israelites who went out from a city and found an abundance left behind by a fleeing enemy and desired to share that wealth with fellow citizens. In Christianity we have such a good thing now and to come that it would be a shame not to share it.