The DAX40 is a piece of German financial engineering, aka not fair to compare to the S&P500: the DAX40 excludes a large part of public German corporations + as a price index it includes distributed dividends, which causes an unfair advantage when compared to a price return index like S&P500.
[0] https://www.google.com/finance/quote/.INX:INDEXSP?window=5Y
[1] https://news.ycombinator.com/item?id=29508238