Well, the reasons can be complex. Poverty is a significant factor. If she is pregnant and has no income or savings, she can't afford a proper place to live. Also, there might be problems with her family relationships. Maybe she has been kicked out of her home or has run away from an abusive situation. Additionally, lack of access to social services like shelters for pregnant women can also force her to seek shelter in Walmart, which is always open and has some basic facilities like restrooms and a bit of warmth compared to the outside.
One reason could be homelessness. If she doesn't have a place to stay, Walmart, being a large and accessible building, can seem like a shelter. Another reason might be lack of family support. Without a family to turn to, she may have to find a place on her own, and Walmart provides a relatively safe environment.
There are several possible reasons. First, financial difficulties. If she can't afford housing, Walmart becomes an option as it is a public place. Second, she may be estranged from her family or friends and has nowhere else to go. Third, it could be that she is in a new area and hasn't been able to find proper housing or assistance yet, so she takes refuge in Walmart.