Judging from your name, you must not be very intelligent. Some of these exotics are not gainable through the bounties. So in other words, instead of just waiting for a random drop and get lucky to "earn" your exotic, they gave you the option to "earn" those strange coins and save up to buy that exotic you haven't been so lucky to "earn" in a random drop. See what I'm saying? Or should I get more clearer?