Final answer:
The demand for plain language began prior to the Plain Writing Act of 2010, arising from societal shifts towards clear communication, especially in legal texts, alongside the evolution of mass media and growing cultural diversity.
Step-by-step explanation:
The Plain Language movement, exemplified by the official Plain Writing Act of 2010 signed by President Barack Obama, was a significant step toward simplifying government communication to make it more accessible to the general public.
Before this formal recognition, there was a societal push towards using language that the average person could understand, particularly in legal and government contexts.
This change came as a response to the recognition that laws and regulations could be expressed more efficiently if written in a manner that was clear to all.
Concurrent with the act of simplifying language, there were also cultural shifts towards inclusivity, like the 1974 "Students' Right to Their Own Language" declaration, and technological advancements that introduced new terms into everyday language.
Together, these factors contributed to the drive for plain language in an age marked by the rapid evolution of communication.
Historically, the movement for plain language paralleled the development of mass media which fostered the consolidation of diverse dialects into standardized national languages.
The desire for plain language has also been evident in the recognition of the language rights of growing and varied populations, an issue underscored by the debates over the designation of English as the official language in various U.S. states.
Overall, the demand for the use of plain language has its roots in social, technological, and political changes, and is deeply intertwined with broader cultural evolution.