Max Verstappen was penalized for his crash with George Russell in the Spanish GP, but why wasn't he disqualified?

In a post on social media Max Verstappen concedes he made a ‘move that was not right’ in the Spanish Grand Prix

After Max Verstappen’s collision with George Russell in the Spanish Grand Prix, the Dutch driver made a shocking remark. In a battle for fourth with just three laps to go, Verstappen collided with Mercedes driver Russell at Turn 5.