Oh yeah has been a common expression of approval in English for decades, and short voice clips of the phrase became popular reaction sounds on soundboards, in streams and in meme edits. The two words work on their own without context, which helped the clip spread as a quick response to good news, wins and funny reveals. Creators reuse it because it is instantly recognisable, fits almost any upbeat moment, and can be dropped into a video without explaining the joke to the audience first.