Why did President Grover Cleveland refuse to sign the treaty that allowed the United States to annex Hawaii?

He was an anti-imperialist and believe the US overstepped in Hawaii.

The marines had forced the queen of Hawaii to give up her thrown and took over the island country. They brought an annexation request to Congress and before it could be considered, Cleveland removed the request from consideration. He believed the US overstepped and stepped on the rights of the Hawaii people. Cleveland tried to put the queen back in power through his presidency but eventually McKinley would push through the annexation during his presidency.

Cleveland learned that the treaty did not have the support of Hawaiians