It probably has to be due to the watch time difference.
My first channel exists longer and has the video's without rehashed content immediately afterwards (videos are around 3 to 4 minutes length. Currently a little under 15 million views over the last 30 days.
Now my second channel with the exact same video's, very similar thumbnails, titles, etc but the content is between 10 and 12 minutes long. Currently 150 million views over the last 30 days (ten times my 1st channel!). Because the videos are over 10 minutes I can run more ads which also doubles the revenue per view.
With the same content, same thumbnail designs, same titles, etc the only variance is video length and look at the difference in success rate!