The bill's name is an acronym for "defending against imitations and replacements of yogurt, milk, and cheese to promote regular intake of dairy every day." (It's not the greatest acronym, though, given that "milk," "cheese," and "day" are left out of it.) Its proponents are worried that the dairy industry is losing customers to people who are misled by dairy alternatives' marketing.
The politicians didn't get this from nowhere. Farmers themselves have been complaining about competition with dairy alternatives. "While imitation may be the sincerest form of flattery, the increasingly common practice of labeling beverages as milk when they quite obviously are not is wrong and misleading," dairy farmer Brad Nevin said in the press release.