Broken down by the replies we have so far.
1) Graphite is lighter
2) More accurate
3) Can cast further
4) Makes a better longer rod
5) Cheaper/Easier to make
6) Marketing
Kind of makes you wonder what the heck we are all doing fishing with this obsolete material. Not
Personally, graphite has become my last choice material for when glass won't get the job done. I mainly fish for trout, and in the past three years I've only
needed to use a graphite rod once. That was on a large lake in 30+ mph winds, and even then I caught a fish on glass first just to know that I could (also to feel a large Pyramid lake Cut. on fiberglass
).
Mostly I prefer using it because I enjoy the casting and fish fighting qualities of fiberglass but I think there are some technical advantages.
Short rods: I'm pretty sure most would agree that it's easier to find a great taper in the 7' and under category. Also, whatever superior qualities graphite has becomes negligible for the type of fishing you are doing with a rod of that length.
Tippet protection: Of course it will depend on the taper but glass lends itself to this ability better than any of the other materials. You can land a large fish with light tippet on graphite but it will take greater concentration and perhaps a bit more luck. The softer nature and flex of glass protects the tippet better, and allows the fisherman a little more reaction time when countering a fishes runs and lunges.
Heavier line-weight versatility: (IMO) This is the quality that makes fiberglass the best candidate if you could only own one freshwater rod in any material. Fiberglass allows you to use a heavier weight line than graphite would for the same conditions. For instance, in trout fishing you could use a 6-7 weight rod without giving up much delicacy, and be able to enjoy the fight of whatever size fish you were catching. Add to that all the advantages of a heavier line, e.g., better in wind, ability to cast larger/heavier flies, still able to cast smaller flies (while having the needed tippet protection), distance, better able to control large fish, and did I mention fun with fish of all sizes?