Perhaps the better question would be to ask what makes a fish bite rather than why they wont bite. Fish are animals and just like all other animals they get hungry. Empty stomachs will drive a fish to feed. But the savvy angler knows that there are other factors that will entice a fish to strike, even when they arent hungry.
All kinds of projects and studies have indicated that fish feed more and better in a moving water situation. Tidal water movement and current are major keys to the feeding effort.
You may have experienced this yourself. On an outgoing tide, the fish are biting and you are catching them at a regular rate. Then as if someone turned off a light switch, they stop. If you paid attention you would probably see that the current stopped with a change of tides.
Current, or rather lack of current will turn off a bite. Even offshore, where you may not realize it, the current will make a difference. A slack tide with no current, while really good for getting a bait to the bottom with very little weight, usually means no fish. The fish finder marks fish all over the bottom, but with the exception of small bait stealers, you cant buy a bite.
Weather conditions definitely affect the feeding habits of fish. As the barometric pressure drops, indicating a storm or low-pressure condition, fish will feed. Storms and low-pressure areas (hurricanes are the ultimate low pressure) mean that the water will be stirred. Fish seem to realize that the dropping pressure, sensed by their lateral lines, means stirred water. They tend to feed ahead of the storm because they will not be able to feed as well in the murky water following the storm.
You can witness this for yourselves ahead of a major thunderstorm. These are low-pressure cells in their own right, and as they approach, the fish will turn on and begin feeding.
After a cold front passes through, high pressure invades the area and the fish seem to get lockjaw. That is probably because they feed heavily as the front and low-pressure center passed through. Now full, they tend to ignore baits presented to them.
In a shallow water setting, water clarity can play a huge part in getting a fish to bite. Long casts from a position well away from the fish are usually required to keep from spooking the fish. As a rule of thumb, if you can clearly see the fish, you will probably have a hard time getting them to bite. Remember, they can see you and your boat as well.
So, if the tide stops running and the fish stop biting, take a break, eat some lunch, and get ready to move to an area that will hold fish on the opposite tide. Learning to move and change with tide and weather conditions will help you put more fish in the boat.