Dota cosmetic items are awarded periodically for a playing and completing matches.
If you feel that you have encountered an issue with Dota's item system, please report the issue via the Dota Developer Forums.
Timed drops are awarded to players simply for completing matchmaking games; win or lose. The type of items you can receive are full item sets, bundles, treasure or Arcanas.
Steam and Dota accounts that are currently in any of the following states do not qualify for item drops or achievements:
In some rare cases, a game may be discarded prior to rewards being granted. Unfortunately, in cases such as this, there is no way to restore these rewards. The game and achievements will need to be completed again.