Why are mushrooms safe for everyone to touch at the supermarket?
A major reason produce can be sold loose without tongs is that you're supposed to wash it just before preparing it anyway.  You couldn't wash your baked goods. How effective this washing is, is of course another matter now we don't have to wash the mud off and a token rinse is probably typical. 

Some produce, including mushrooms but also strawberries etc., could easily be damaged by tongs anyway.