Well, you don't flyfish so you don't understand the clear advantages a longer rod gives the flycaster on many trout streams. There are a number of advantages but longer casts and better line mending capabilities are two of them. Longer rods also make for excellent nymphing presentations. Actually a 7'6" is a bit short for an all-around 5 weight rod. 8' or 8'6" is better. A 9' rod is an excellent choice on larger trout streams like the Upper Delaware area or say the Lehigh where longer casts are often necessary as well as a rod capable of punching through the wind.
I don't fly fish huh? Are you kidding? I have been fly fishing since I was 5. My dad has been fly fishing for the last 45 years plus. He has been making rods for the last 30 years. He has also ties flies for numerous shops, and has been asked numerous times to put on seminars. We only use flies for trout and do a fair amount of fly fishing for other species as well.
I don't know if it is the geographic area or what, in the area I fish, you don't see people using 9ft plus rods for trout. There are not many "large" streams around. Some of the waters we fish are The Yellow Breeches, Falling Springs, Marsh Creek, Little Marsh, Middle Spring, The Conocacheague, Mountain Creek, and The Conodoguinet. Most of those, are not very wide.
I own two fly rods for trout, a 6' 4 weight, and a 7'6" 5 weight.
For those of you that simply answered my question, thanks! For those of you that don't think I fly fish, have fun with your 18ft leader!