A good portion of that is "the times". While I agree about not putting up any new statues to Custer, tearing down the old one gives up an opportunity to teach kids about those "times"; Manifest destiny, the Indian Wars, the Civil War (which is where Custer
the Yankee got his reputation

), etc. Tear it down, turn it into a park and all that's left is people talking about their Facebook page.
Another problem is money. Putting up a memorial to Native Americans is good but who's going to pay for it? The statue for Custer already exists. It might be easier to raise the money of a Native American memorial if it's an "addition" not a controversial "replacement".