Why is it so important to Christians that Mary had to be a virgin?

Because that is part of their bizarre obsession with sex.

So that there is no doubt she gave birth to our savior and a heavenly child not an earthly one

As another has said, a virgin birth to "fulfil prophecy" involving a disputed passage in the OT (that would seem only to speak of a young woman, not virgin)

Again, some scholars have argued that in the ancient world it was believed that it was purely the seed of a man that brought forth birth. After St Augustine taught that original sin was passed on to each human being in the sexual act this consolidated the necessity that Jesus be born of a virgin, as if not so, he would himself have inherited original sin and thus not be the sinless offering to the Father.

Once it became known that a woman played a necessary part (her egg) as well as the sperm of the male, along came the dogma of the Immaculate Conception (of Mary), now a necessity to once more preserve the sinlessness of Jesus.

There is two main reasons. The first and most widely known is that her virginity fulfills a prophecy in the Old Testament. "Therefore the Lord himself will give you a sign; the young woman, pregnant and about to bear a son, shall name him Emmanuel." Isaiah 7:14

Second reason is that Mary is the new Ark of the Covenant. I can explain this further if interested.

Nothing in the Bible is just for marketing or dramatics.

I don't think it's very important it's just they hold their faith on it. If the stories faults then that means there whole life's philosophy is false. The Virgin Mary is a good example. I love the story of the Virgin Mary and I do pray to her sometimes.

The smokin gun in my own faith growing up in the Mormon church is that Joseph Smith prayed and two angels appeared I think they were Jesus and John the Baptist, but I don't remember for sure. This wasn't they way he originally told the story this version didn't appear until the church was already established and he was much older. I don't believe that Joseph Smith prayed into the woods asking God what is the true church and that destroyed my faith in the Mormon religion.

Jesus had to be born without inheriting the sin nature... Jesus was a creation of the Holy Spirit who caused the start of Jesus life in Mary... I don't know if Mary had to be a virgin or not.. I am sure The Holy Spirit could have caused Mary to become pregnant either case..

I would say it was important to establish that Jesus had no genetic human dad.. So as to show that His actual Father was God...

So it was not done this way for any dramatic touch.. It was just to establish that no human man fathered Jesus.. That Jesus was born never inheriting the sin nature of humans.. He was without sins..

Dudes prolly thought tight vagina felt better. So added that in as a prerequisite. Women were just considered objects in the past anyways

What's it to you other than to be annoying to believers?

What should be more important to you is how to find happiness outside of this sad, little post of yours.

@InOtterWords Joseph was not his father.

From what I remember they had to claim that to fit a misunderstood prophecy in the OT. But the OT prophecy never actually claimed that. When it said virgin it was simply the ancient term for teenager, not someone that had never had sex.
The Hebrew word is הָעַלְמָ֗ה meaning young women which got translated as virgin which got interpreted as never had sex.
So they screwed up the prophecy in their effort to force it.

The same thing can also be seen in the prophecy where Jesus enters the city riding two donkeys at the same time. But Matthew trying to shoehorn a prophecy as well misunderstood Zechariah 9:9.

It's not important to us at all. It was to God and that's all that matters.