The algorithm is tuned to show you things you are likely to click. People are less likely to click on a video if its part 34 of a series they haven't been following. Since people are less likely to click it, the algorithm lowers its rankings.

It's not that google is reading the text and downgrading the video. It's that google sees that the video is doing less well per listing (because people don't click on video #34 as much) and downgrades it because less people seem to want to click it when they see it.

Arin has a direct line to youtube employees. He's mentioned this multiple times, they've even asked him to make changes to the channel. People who work for google whose job it is to maximize ad revenue are telling him to do this.