It's not. The entire purpose of Tor was for US spies overseas to be able to make anonymous secure communications. They opened it up to the rest of the world, because if the only people using Tor are US spies, it's pretty easy to tell what someone's using it for.

Governments also run a lot of relays and exit nodes for a similar reason. Not to make it easier for themselves to identify traffic. For no one actor to have a majority of nodes, which would make it a lot easier to identify traffic.