"Boiler plate" originally referred to the rolled steel used to make water boilers. Metal printing plates of prepared text such as advertisements or syndicated columns were distributed to small, local newspapers, and became known as "boilerplates" by analogy. One large supplier to newspapers of this kind of boilerplate was the Western Newspaper Union, which supplied "ready-to-print stories [which] contained national or international news" to papers with smaller geographic footprints, which could include advertisements pre-printed next to the conventional content.
A "template" is entirely different -- it is intended to be modified.