Some companies sent out press releases as boilerplates because then they had to be printed as written and without changes. Literal plates are not used for printing today, but boilerplate, or "boiler," text might still be text sent out to be used "as is" which saves the recipient from having to create content.
In contractual law, the term "boilerplate language" describes the parts of a contract that are considered standard.
Even computer programs may contain boilerplate sections of code that are used in many places with little or no alteration. It is used for efficiency.
But why BOILER plate? The term boiler is used for a closed vessel in which water or other fluid is heated. They are constructed of boilerplate, a relatively thick, high quality sheet steel. The metal at least resembles the sheets used in the printing process. Those boilers also typically carried a smaller plate of embossed metal (as shown here) that told who had produced the boiler.