You can change a banner. A new banner can have a new message. A new banner can have new colors and new dimensions. As time passes, events and sales and promotions change. So can that big banner.
Big banners are relatively inexpensive.
They hardly require research and development. The materials are readily available. Rocket scientists are not needed to make even the biggest banner. The big banners do not require the intensive work and time of an army of sign professionals. There is no major fabrication, no electrical work, and no real installation woes.