Touring bikes are built with heavy loads and steep hills in mind, and they need wide gearing. It is not uncommon for a touring bike to have a triple with a 30 or smaller ring in front, and a 32 ring in the rear. These gear ratios can't be served by road components (the lowest you're supposed to go with, say, 105 components is 30/28, though in practice there is some wiggle room), so manufacturers go with MTB components.