<p>Usually its a mix of personal preference and to support their fellow NND ~ites. A lot of Odorite's and Utaite's are friends and in result they prefer to support their friends and use their friend's covers in their dance videos. It usually doesn't really have to do with popularltiy or anything.
</p><p>The reason why they probably don't use covers for non-vocaloid songs (such as an idol group dance covers or kpop dance covers) is probably because their friends/people don't do song covers of these songs as much and in this case it is just more common/popular to dance to the original version of the song.
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