You'd be amazed at how many millions of dollars in accounting liabilities there are in these programs. There are many reasons stated throughout this thread and they're pretty much all valid. Especially in the US for instance, pretty much ANY activity even if it's a tiny withdrawal to purchase an ebook or whatever, will keep your points alive. A co-branded credit card often helps with this. At the end of the day, if you can't even be bothered to do that, you're not very "loyal" in the first place, and the program isn't meant for people like you.

But at the end of the day, all expiration policies are tied to the bottom line, as in "the accounting sense". An actual accountant or finance person can correct me, but the way I understand it is that reducing "liabilities" by expiring points basically improves the balance sheet by making it look like you owe less money which improves credit, EBITDA, debt to revenue, stock prices, etc. etc. All things that are very important to investors and shareholders.