I guess the reason was mentioned above - they can write down those "dormant" points from their balance sheets if they expire. OTO if there's some activity on the account every year, it shouldn't be considered as dormant - but of course making the points expire not only lightens the balance sheet, it actually may save them some rewards in the future. Not too customer friendly - if a not too-FT wants to collect points for that family trip to the US or Japan (or even to Spain or France), it's all but impossible to do in 3 years.