When I moved into my current house, the grill pan was in a disgusting state. I thought that nobody actually used it (the house is shared with 2 other people) and would occasionally move it out of the kitchen because of the smell. I realised it was actually still being used after leaving it outside one time and the following day finding it back in the oven.
I don't know how long it has been since the pan was cleaned or the foil changed. I moved into the house 2 months ago and it certainly hasn't been done since then. There is also a baking tray (not pictured) which is in a similar state. It's covered in foil and rancid fat and the lumps of food/batter/breadcrumbs which drop off when you cook things in the oven.