While I agree that the pivot to video was a massive turning point in the dumbing down of political discourse, I think it’s more to do with the pace and passive nature of video/audio: the people are getting news and ideas at the cadence that the broadcaster deems appropriate instead of at the pace of the listener which would happen in reading or face to face transmission.

If something was missed entirely or misunderstood it is far more tedious to try and hunt down the segment that needs reiteration than it is to read it again (or ask for clarification). This means people that miss something will just try to pick up any context later in the broadcast and if the broadcaster doesn’t deem it important or relevant (or maliciously omits it), the listener has no further interaction with the idea. And then the idea is lost beneath the rest of the news agglomeration.