With a population 20,000 less than the normal 60,000 required for statehood, Congress nevertheless admitted Nevada as the 36th state in the Union. They wanted the votes. President Lincoln's reelection apparently hinged on the support of the Republican-dominated Nevada Territory. Basically, on 40,000 people, who couldn't all vote.
Never let it be said that Congress doesn't know a gold mine when it sees one. Or in Nevada's case, the 1859 discovery of the incredibly large and rich silver deposits at Virginia City.