Many prefer the Kingdom Hall because of the requirement that ALL of the wedding party is "in good standing".
Many do not care. Use of the Hall requires approval from ALL users of the hall (every congregation) that there will be no schedule conflict...a real pain if multiple congregations and languages use the Hall.
Many prefer a reception site where food & alcohol can be served, and that is located near where most of the attendees live (family and real friends). Having a wedding in the Kindom Hall guarantees a crowd of hungry judgemental acquaintances/locusts descending upon the reception and eating everything in site. $$$ :).