I once wondered the same question as you, a kayak for fishing? I assumed they were too small, uncomfortable, a pain in the rear to load, didn't allow you access to fishable areas, etc. I couldn't have been more wrong. It took me a few months to get the hang of kayak fishing, but when I did, everything else just kind of fell into place. My goals are to help you become a better kayak fishermen, so that it doesn't take you as long as it took me to start catching a lot more fish.
One reason most people use a kayak for fishing is that you are only able to bring a limited amount of gear. You are forced to load your safety gear first, and fishing tackle last. This helps you learn what baits and techniques work, and leave the fluff at the house. You can usually only bring 1-2 rods, instead of a full rod locker found on most big boats. This helps you become a better angler, by forcing you to use only the techniques that work. You'll get to take these tips back to your big boat buddies, and be the man! (Or woman!)
I also always assumed that a kayak for fishing would be very uncomfortable. I didn't have a clue how people sat in these things for 8 hours a day in the blistering heat. After a few fishing trips, I had raw legs, a sore back, busted up elbows, and was just in pain in general. I just about gave up the sport. Taking a 2-3 month break through the cold season, I learned a few things that I knew would help me in the upcoming fishing season. One of the things I learned was about making the kayak more comfortable. When the weather started heating up, my need to fish took over, and off to kayak fishing I went. This time with a renewed spirit, and a few modifications to make the kayak more comfortable.
Most people think of fishing, and think that you have to have a big boat to get to the hot spot areas to fish. They can travel all day long, searching for the one hot spot, not ever realizing that they have passed up more fish than they will probably ever catch in their life. Using a kayak for fishing, you can't travel 20-30 miles a day to find the fish. You gotta anchor up, and fish the area you are in, move a little bit, and repeat. You learn so much more using this method, fishing becomes more enjoyable instead of wondering "what lure do I use" "where do I fish at" "where are the fish". Fishing requires patience, and being in a fishing kayak teaches you that better than any stinkpot can. Once you realize that you don't have to fish the spot where you think the fish are, and start fishing where you are at, you will catch more fish! I catch a bunch of fish just sitting in my kayak waiting for my buddies to load theirs.
There is a little more work involved in using a kayak for fishing. You can't just throw your rods into the boat, and back the truck down the ramp. I use a small car to get my kayak back and forth, and am limited in space to what tackle I can bring with me. When you get to where you are going to put in, it does take an extra 10-20 minutes to rig the kayak, depending on how much gear you brought with you. It is a little inconvenient, but rigging your kayak should be a fun experience. After all, this is your personal boat! As long as you take pride, and have fun rigging, the extra time in the morning doesn't matter much. Now after a long day, unloading is a different story! You will learn about that though, just drink water before you get off the kayak at the end of the day! It will keep you from being so run down.
Using a fishing kayak also means complete stealth. When you are in a big boat, people are talking, banging against the deck, dropping things. These noises may not seem like much, but they are amplified through the boat down into the water. Sound travels in water in waves, so fish feel it. Even if this doesn't scare them off, you will make them nervous, and most animals won't eat when they are anxious. Would you? So if you wondered why you should use a kayak for fishing, I hope I have helped you reach your goals!