It's simple really, your cooker is a giant heat storage unit! When the insulation is poor it uses more oil because the heat is radiating away out the hob, lids and even the sides without ever getting to the ovens. Really no part of your cooker should be too hot too touch, if it is that is an indication of insulation problems.
In the picture below you can see an Aga range cooker that had been moved within a property. I suspect that some of the vermiculite and thermal blanket was 'lost' during the move and the chaps responsible simply popped the top back on knowing no one could see it anyway! What was left of the thermal blanket was a mix of old and very old insulation with some basically in a dust like state thanks to the constant heat exposure.
Once I had removed all the old thermal blanket the first step was to top up that vermiculite, here is a picture that shows how much of the hotplate 'barrel' was exposed to the air. This barrel is 600 degrees, imagine how much heat and energy was coming out sideways and being lost!
Here though is a nicely topped up cooker packed full of lovely vermiculite!
The final job is to replace the thermal blanket that ties all this together and finishes the job of insulating the hob. You can see how thick the blanket is, it is compressed by the heavy hob that sits on top of it. There is even another layer to go on after this picture but for some reason, probably had the cricket on in the background!, I forgot to take a picture!
These pictures show only a small part of the job of making a range cooker efficient of course. Renewing the insulation in the lids and doors is crucial too, how hot are your range cooker doors and lids to touch?!, as is smaller jobs like plastic door washers and the like. Working on range cookers is not an exact science, more like an artform!, but there is no doubt this range cookers will run cheaper and cook better than it did before, probably by quite some significant margin!