The traditional construction method for wood doors is to combine stiles (the vertical components) and rails (the horizontal components) to create a door style.
Fiberglass doors mimic this construction method by including stile and rail lines on the models.
Doors with glass have a lite insert placed in the door. For example, a full lite can be created by taking a 6-panel door, cutting the panels out, then inserting the lite. This will create a door model with stile lines.
Fiberglass doors made without stile and rail lines are known as flush doors. The same process of adding a lite insert can happen meaning the door model will be without stile lines.
While having a lite in a flush door is a possibility, this door will look less like a wood door and be less architecturally correct.