When I ran Create Tile Package, my input tiff was in UTM Zone 13, and the output tile package was in Web Mercator (the project Map was in Web Mercator). I think this is where something went wrong. Just now I used the Project Raster tool to project the input tiff from UTM Zone 13 to Web Mercator. Then I used the Create Tile Package tool to create the tile package from the projected tiff, and then published it to AGOL, and now it is visible!