Because Mary was the New Eve, the one who would crush the head of the serpent.
It was not out of disrespect, etc. as you are thinking.
By the way, Jimc, I would recommend you read a good Catholic commentary on Scripture. Obviously you are interested in Scripture. But there are many difficult things in Scripture "which the learned and unstable wrest unto their own destruction" -- so ANY reader of Scripture needs a guide.
Read a good, traditional Catholic commentary and you will understand a lot more about Scripture.
Sincerely,
Matthew