So every product has a sweet spot and for porch gliders that is definitely the 5 foot length. In both outdoor swings and gliders there is a simple rule of thumb for seating. View our chart below.
2/3 Foot - seats a single adult
4 Foot - accommodates two adults
5 Foot - comfortably seats two oversize adults or 3 adults
6 Foot - "The Big Enchilada" can seat up to 4 adults.
Take a look at a normal 5 foot outdoor glider below offered by Amish Creek.
So now that we got that out of the way you can see why 5 ft porch gliders is the sweet spot. It's flexible for more spacing for two or seating for three. Most manufacturers have seen this trend over the past few years and are moving away from the traditional two person length. As a customer you have to understand this will result in a slightly higher price point. Additionally, the 5 foot shipping cost is about double that of a normal 4 foot length as UPS and FedEx dimensional weighting applies. So if you are looking for a honest answer on the price difference there it is. But don't let this stand in your way of finding the best one for you. Refer to our chart, check your budget, and get a glider that works for you.