Because you can see how, after H and He, you do 2 loops of 8 and add the transition metals to the next 2 loops; then you add the lanthanides and actinides to the next 2 loops. And can easily see how the superactinides guy in the extended period table
xkcd #2913: Periodic Table Regions ( imgs.xkcd.com )
xkcd.com/2913...