"The first person to make peanut butter popular was John Harvey Kellogg. He was a vegetarian, and in the early 1890s, he invented a way to crush nuts between two rollers to make nut butters as a substitute for cow’s butter and cream."

Thus, his intent was to replace dairy butter. The federal definition of butter was put in place in 1906. Apparently a definition of "butter" wasn't an issue before dairy interests gained influence. The Oleo Margarine Act of 1883 was put in place to protect dairy interests.

This issue revolves around market share and profit. Plant-based products are cutting into dairy profits.