Probably because of the lack of incentive to do so. Even so, regardless if the drop-rates is known or not, people really need to have this mindset of what Zathroth said. As a f2p, are you really going to use your limited amount of coupons on something that is not guarantee? Learn on how use your coupons effectively rather than gamble it. In case people were wondering, people that were present when jonin and masked man appeared in our server should have gotten at least one of them for free by now via free points from events.