The script, if you haven't seen it:
தமிழ் தமிழர்களினதும் தமிழ் பேசும் பலரின் தாய்மொழி ஆகும்.
And the answer:
Another writing material that was very common in ancient India was palm-leaves (or Tada-patra) (the earliest manuscript belongs to second century A.D.). Palm was originally indigenous to southern India, where it was preferred to birch-bark because palm-leaves are so abundant in the south. Ink was introduced in the south rather late. The letters were scratched on the palm-leaves with a sharp, dry stylus. The manuscripts were made legible by dusting it with black powder, which remained in the crevices and made the writing visible.
For this reason the south Indian scripts are much rounder and more connected than those of north (since the leaf would be torn with horizontal lines).
— Pijush K. Ghosh, "An Approach to Type Design and Text Composition in Indian Scripts" (foreword by Don Knuth!)
Similar material constraints affect the shape of the North Indian scripts.
In our era of rapid technological change, we see a clear relationship between material factors (cars, airplanes, the Internet) and cultural change (suburbs and malls, international travel, social media). We can add this surprisingly ancient example to the list.