Unless you are in business to put your best customers into airline seats at full retail prices, you would probably rather give your customers your own products, which cost you a lot less. Airline miles are inexpensive. Airline miles are not cheap. By giving your customers airline miles, you end up paying full retail prices to place your valuable customers into an airline seat, plus paying to issue those points unless you struck the deal with the airlines yourself. So you actually pay twice, when you don't have to pay at all.
Generic currencies are a good alternative to airline miles.
Not at all. There is a big difference between generic currencies and your own currency that you issue points for. Generic currencies operate the same inefficient way as the airline mile. Program operators who market their own currency are out to compete for your customers' wallets just like the airlines. PassPoints is the only company that lets you issue your own points.