Strongly recommend "Amusing Ourselves to Death" if you're interested in exploring this question further. It has a strong bias towards reading but does a very thoughtful comparison of various media. We don't need to consume content of any form, of course.

In my mind reading is more similar to thinking than watching. I have no basis for this but it just feels more mentally active. Of course it could just be my biases but I feel it is much easier to passively watch or listen to something rather than to read. But also I would say from my own experience writing and speaking promote “neurological health” even more so maybe the method of consumption is not as important as long as there is sufficient synthesis and thought on the other end.

We don't need to, in the sense that we survived without it. However a key difference between reading and passively listening or watching is the ability to dynamically vary the pace and re-thread ideas together. E.g. to slow down during complex parts, e.g. involving lots of pronouns, tenses, or familial relations, to move your eyes around on the page, and even to pause a moment to quiz and rehearse to ones' self on the material. To even attempt to connect it with existing ideas from other sources.

While theoretically possible with non-linear media like videos and audio playback, the fluidity of reading is far superior. Thus, passive consumption leads to many fragments of ideas remaining atomized and not sticking. In contrast, reading allows one to efficiently stitch numerous ideas together.

The point of reading is not to become convinced or apprehend a single summarizable point. Rather, it is to fill one's memory banks with thoughts, experiences and ideas that can be combined with other ones and synthesize new information.

Contrast wandering though a botanical garden, reading labels and looking at plants on the one hand. On the other hand, picture a slow-moving bus that rolls continuously through the garden. The bus may pause from time to time, but mostly it remains on the path, letting you watch things go by from a distance. Both means of travel "get you through" the garden, but the self-pacing version allows a personal connection to the information.

So it would be convenient for a farmer to have his animals illiterate, yet capable of listening passively to commands over loudspeakers. And to the farmer, it would be inconvenient for these animals to learn to read and explore material on their own which would eventually lead them to an awareness that they don't want to be fenced in, farmed, and eaten. So you can see why some questionable leaders are comfortable with illiteracy as a means of control. While others seek to empower humanity through encouraging reading.

written language is just much more information dense than talking. the goal of writing is to distill someones thinking into the most effective vehicle to transfer it without time constraints.

i imagine cultures that refined oral histories over generations ended up at a similar place, but that doesnt really happen nowadays. It really is true that instead of listening to a 3 hour podcast about a topic, you could probably get all that info within 30 minutes of reading.