This is very normal.
This also happened in our house.. Stay at home mom. That will tell you most of the reason. We do everything for these children, so naturally, they are most comfortable with that person. I have a friend that is a "Stay at home dad". His wife works all of the time, so he is the preferred parent.
His children are now entering High School and the kids never ask their mom for help. It is just a habit.
My husbands feeling would be so hurt when our daughter would say, "No Daddy", "Yes, Mommy" when she would refuse to let him pick her up. Or refuse the food her served her, the toys he would try to play with her. It was awful. We made sure to tell her, it was hurting daddy's feelings when she would not let daddy hold her, or help her.
We made sure to have just "daddy time". I would leave the house or send them out on their own to "Not just run errands!". They went to the park, to events, to play with the neighbors, to eat at a restaurant (nothing fancy, Taco Cabana, McD's, Central Market). I would remind my husband to do things "His way" and we would call those times, "Dads way". This was a way to show our daughter things could be done dad's way and it was ok. Girls are also bossy, so like things done just the way they want it or are used to it, so we need to remind them, it is ok to do those things a little different. Have him bathe her and read to her at night. To make it easier, you may need to leave the house. This is a good time to do your shopping, see a movie or go for exercise.
It also helped that we had a little neighbor who had a huge crush on my husband. She would beg my husband to hold her or play with her. Boy our daughter caught on to that real quick.