I don't think the intent was to provide this function, turning the switch to the left and pulling the knob to turn the fog lights on, at all. A better question would be why does the first click to the left allow the fog lights to come on at all?

The answer is probably something well thought out, as, in the days this switch was designed, function was more important than cost or styling. But at the moment it seems the first click is an anomoly of the switch design that might make it more complicated to undo. Jim

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Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)