If you are just playing against bots, the challenge is arbitrary. What would top 10% actually mean? 5000 ELO? Albeit, the ranks are slightly arbitrary already as the matchmaking algorithm significantly influences your competitive experience. But you know when you get higher rank, you have proven you are better than increasing amounts of real players. If every person was actually playing a single player variant of the game (matched against bots), the reward for climbing the ranked ladder is significantly diminished.

In multiplayer games much of the fun in winning is someone else losing.