Great question. Welcome to the forum!
I always thought that it was a way to just showcase that he’s done a lot of stuff, and not like a complete discography. To me it seems random what’s included and what’s left out (or maybe forgotten). I think that new Parliament/3GP vinyl is also missing, but that’s perhaps because it hasn’t been updated in a while.
I noticed that’s it only possible to scroll down a little bit, after that you can only view the covers one by one by pressing the next button. Not really easy to get a good overview. 
Other discographies that come to mind are the one on Danny and the one on Bernie. Both have chronological order.