Look. It's simple. The semiconductor business is a cut throat one, and Olympus has to order a sizable quantity to justify a production run. Otherwise, your Pen cameras will start having as much as a 10-25% price increase, or you will be stuck with the same sensor for a long time.
Asking for a new sensor is difficult simply because of the cost etc. Perhaps why Olympus is still using a 12MP sensor is because it has a huge backlog of 12MP sensors waiting to be used because they had to buy lots of it to keep the prices low.