Why will the pilot light not light?

No. The pilot light uses a thermocouple(safety device) to let the main gas valve know that the pilot is lit so that the main gas valve can operate safely by not letting the main gas valve turn on without a lit pilot light. This way, in no way can the main gas valve turn on until the heat from the pilot light causes the thermocouple to produce an electrical current which allows the main gas valve to operate when the thermostat switch closes.

Hi pilot ligh lit fitted new thermal cupling gas pilot lights hold down switch for over 2 / 3 minutes butgas pilot goes out

Most gas ovens that aren't electronic ignition usually have a pilot light.
Usually one in the oven area and one for each burner. (Sometimes shared between two burners.)
These pilot lights must lit at all times...otherwise it won't light up and you'll smell gas.
Usually the pilot light is in the very back of the oven and can be seen with the broiler drawer opened.

There is a small set screw located at the pilot light assembly in the oven and also at every burner.
This allows you to adjust pilot light up or down, thereby letting you set pilot light flame to a level that doesn't get blown out by a draft...or you can turn it off completely.

If you use that set screw to turn off the pilot light gas, you'd need to strike a match to light the oven or burners everytime you needed them.

Instructions

1. Access the burners inside your oven by removing the access panel in the front of the oven or by opening the broiling drawer, depending on your particular model.
   
2. Determine if the pilot itself is lit, since some ovens have a small flame on the pilot at all times that then grows and extends to the burner when the oven is turned on. The lack of a pilot flame indicates the oven thermostat is malfunctioning or there is a problem with the gas hose. Check the pilot itself to see if it is clogged with debris or grease that could be preventing the flame from staying lit.
   
3. Determine if the pilot flame will grow if it is lit by turning on the thermostat. If the pilot flame doesn't extend, the thermostat itself likely needs replacement. If the flame is extending but the gas valve is not opening, the safety valve could be dirty or defective. The flame should be blue in color. A yellow flame indicates the pilot is dirty and is not burning hot enough to get the main burner to ignite.
   
4. Light the burner on the top of the oven with a match if the igniter doesn't appear to be effective. If it lights manually but will not light automatically, the igniter is likely faulty. Do not do this if there is a heavy smell of gas in the kitchen, since there could be a risk of a fire. In that circumstance, turn the oven off, ventilate the room and call a technician.
   
5. Listen for any sounds of gas hissing or a clicking sound indicating the oven is trying to turn on. If there is no response from the oven at all, the gas may not be functioning properly and will need to be examined by a technician for safety purposes
   

Get the oven checked out by a professional, if you have a gas leak you can easily blow up the entire house and you with it. I think you have a faulty gas valve based on what you wrote

I have a whirlpool accubake system / super capacity 465 oven ... the top burners do fine...but my oven pilot went out... and I don't know how to re-lite the pilot... the owners manual doesn't help ... it doesn't show anything a layman could understand ... no visual illustrations ... when I turn on the oven ... the display shows that it's been activated... it clicks a couple of times but does not light ... what is a simple way to re-light the pilot? thanks, A

It was an electric ignition
Thank you

Relighting Your Furnace's Pilot Light
- Turn off the gas at the main valve at your utility box - Wait five to ten minutes for gas fumes to waft away - Get a long match—yes, a fireplace match, not a standard match - Set the gas valve on your furnace to "pilot" - Press the red button as you hold the match to the pilot valve - Keep pressing the red button for 30-60 seconds so the pilot can heat the thermocouple. Release the button and see if the pilot remains lit - If pilot goes out, wait five to ten minutes and repeat the process - Once the pilot stays lit, turn the main gas valve back on - If the pilot light continues to go out, call a technician, who may need to adjust or replace your thermocouple or adjust your pilot

When you smell gas...is it all the time? If so, this is dangerous. If it only happens when you're trying to start the oven, no problem. Push the red button and hold it while lighting the pilot. Hold for 30 REAL seconds more. Release. The pilot should stay lit. If not, get a service tech.

replace the thermal coupling on the pilot make sure it is in the flame of the pilot it looks like a copper wire or tube if its bad it wont open the gas valve after the pilot heats it up