Silly title. One could just as well ask why MB charges so much for a 4 door sedan that is so similar to other 4 door sedans that cost less than half.
Engineering and research and innovation all cost money.

You'd prefer to go back to the days of "more road-hugging weight"?

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1982 300SD " Wotan" ..On the road as of Jan 8, 2007 with Historic Tags