My reason is that Fuji is the only company that produces a reel seat that will securely hold reels from almost any manufacturer. They use a small nylon foot inside each hood on the reel seat that conforms to the shape of the foot of whatever reel is placed in it. I don't know of any other reel seat manufacturer that does this. Metal reel seats offer added strength over graphite for those applications where extremely large fish are expected to be caught. The metal used in the construction of the reel seat can make a difference in strength, weight and the resistance to corrosion of the seat.
Some metals used in reel seats include steel, aluminum, nickel, and titanium.
Titanium seats can be installed on rods that will be used on heavy duty saltwater rods. They clean up quickly and easily with a quick warm water dousing after a day on the water, and titanium doesn't corrode under exposure to saltwater. The pay off is that titanium costs quite a bit more than its graphite cousin. Single piece fly reel seat utilizing metal hardware and resin impregnated hardwood insert. One more material option to consider in a single piece trigger style reel seat is Dynawood.