Final answer:
The shift from maps as reference tools to communication tools is primarily due to technological advancements influencing their development and use, reflecting societal and cultural evolution.
Step-by-step explanation:
The primary reason why the earliest maps were reference tools but now are mostly focused on communications is due to advancements in technology alongside changes in societal needs and cultural shifts over time. Historically, maps were subjective tools, created from the perspective of the mapmaker, often reflecting political power and territorial conquest. Over time, with the advent of new technologies and a globalizing world, maps have transitioned into communication devices, providing digital data and facilitating online applications. They serve as powerful graphic tools in Geographic Information Systems (GIS) that are central to modern science and help visualize spatial relationships and processes on the Earth's surface.