Options expiring 18/11/15, page-3

Some may be holding onto them until the last minute; some may have forgotten they have them or do not know that those options do not get automatically exercised and/or do not know how to exercise them.

Others (perhaps the vast majority of the remaining unexercised options) may be holding onto them in order to cover their short positions in case there is a spike in the SP. As of 29/10/2015, there were more than 5 million shares short for NRT (http://asic.gov.au/Reports/Daily/2015/10/RR20151029-001-SSDailyAggShortPos.pdf). No dump of options can be expected from those short sellers, because they will eventually need to use those options to cover the shares that they borrowed and already sold earlier.