Shortened performances

[Bruised.Sapphire]

So I've noticed for a while now that when ayu performs a song on a show, the performance is always shorter than the original. Like a song on the single would be 4 minutes but the song and performance gets shortened to 2 or 3.

Is this because of time constraints to ensure all artists on a show will have adequate time to perform? If that's the case, do they shorten the performances for all the artists, or do just some artists get a shortened performance while other artists get a full one?

And does anyone know how they go about figuring out who to shorten?