I think the style arose out of a need to fill a 1-minute video targeted at an audience of low attention-span 13 year olds with 9 additional minutes of CONTENT!

I think the style arose out of a need to fill a 1-minute video targeted at an audience of low attention-span 13 year olds with 9 additional minutes of CONTENT! in order to meet the length requirement for monetization. If the filler CONTENT! is bombastic and sing-songey, it keeps your attention, however vapid it may be.