Change the URL: https://skyline.github.com/<username>/2019
Truly a blast from the past, but not in a good way.
Not the first time that GitHub has hidden features behind URL editing...
Also, it's mostly a toy, so whining about missing UI features is probably a little silly.
Or the simple explanation is that the data from years back is maybe not in all caches and it's a lot easier to launch the feature with the currently already fresh and cached data.