[JetSetWilly]

Because your interstellar equivalent of the CIA can obtain the political capital to prevent a civilisational rival from emerging via subtle manipulations, but it can't obtain the political capital and consensus needed to commit wholesale genocide.

There's a big difference between the scenarios.

[rsynnott]

In this case the subtle manipulations were just a holding pattern while they waited on the genocide; it was going to take them 400 years to get here.