Why does this thrash my GPU?

Graphics
1

The size and surface formats of the render targets don’t matter. Why does switching between render targets increase GPU usage when no changes have been made?

For the record:
Platform: Windows 10 cross-platform desktop project
MonoGame version: 3.7.0.1708
Graphics card: ASUS GeForce GTX 1060 6GB Dual OC

But if you create a new MonoGame project and paste this into Game1.cs I reckon you get the same results (high GPU usage)

Is there any other way of applying a render target than swapping it with something else?

using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Graphics;
using Microsoft.Xna.Framework.Input;

namespace Test
{
    public class Game1 : Game
    {
        GraphicsDeviceManager graphics;
        SpriteBatch spriteBatch;

        RenderTarget2D renderTarget1, renderTarget2;
    
        public Game1()
        {
            graphics = new GraphicsDeviceManager(this);
            graphics.PreferredBackBufferWidth = 1920;
            graphics.PreferredBackBufferHeight = 1080;
            graphics.ApplyChanges();
            Content.RootDirectory = "Content";
        }

        protected override void LoadContent()
        {
            // Create a new SpriteBatch, which can be used to draw textures.
            spriteBatch = new SpriteBatch(GraphicsDevice);

            renderTarget1 = new RenderTarget2D(GraphicsDevice, 1, 1, false, SurfaceFormat.Color,
                DepthFormat.None, 0, RenderTargetUsage.PreserveContents);
            renderTarget2 = new RenderTarget2D(GraphicsDevice, 1, 1, false, SurfaceFormat.Color,
                DepthFormat.None, 0, RenderTargetUsage.PreserveContents);
        }

        protected override void Draw(GameTime gameTime)
        {
            GraphicsDevice.Clear(Color.CornflowerBlue);

            for (int i = 0; i < 1000; i++)
            {
                GraphicsDevice.SetRenderTarget(renderTarget1);
                GraphicsDevice.SetRenderTarget(renderTarget2);
            }

            GraphicsDevice.SetRenderTarget(null);

            base.Draw(gameTime);
        }
    }
}