I think Riot's ideal world is one where every player finds a group of friends that they can regularly play together and improve together. In such a world, the game becomes less about random matchmaking and more about growing as a team. To that end, rewards are geared towards encouraging people to find others to play with.
When Riot says they want to support Solo players, they mean they want solo players to feel like they're able to compete and be evaluated fairly. It's worth pointing out that if bonus IP or key fragments are your goal, there are public chat rooms with other solo players looking to get the same rewards, and you can team up with them for the rewards.