The newer mini-games reward a chest which contains your rewards. The older mini-games however (ie, sanctum sprint) use the old system, where you receive the rewards directly.
Please update the old games to reward chests instead.
The chest reward is much better, since it means I can play the mini-game continuously without having to leave or care about how fully my inventory is. I usually only have a few spaces free (~10), so rewarding chests is a big plus.