Why do the patents on google patents contain 's1' after the patent number
It is only on the end of design patent numbers. The letters after a patent number are a publication kind code. There is an international standard WIPO ST.16 for them but it seems to be special-cased in its use in various countries. That standard and a page on the USPTO web site:
says design patent publications in the US have a kind code of S. I found one other document that shows S1 or S but it looks to me that S is correct.
I see on a google page explaining the format of their XML information that the kind field is two characters and that S1 is for design patents.