The songs do just as good or even better than the actual title tracks. They find an audience outside the groups fanbase. Dope, fever and anti romantic to some extent all did better than their respective title tracks. Fever, a bside was the most streamed 4th gen song last year. Polaroid love is currently Enhypen's highest charting song in korea and has already outstreamed the title track.
If you look at the average performance of a bside you'd notice that they get much less streams than the tt. A tt would be at 100m streams while the bside would be at 15m if you're lucky.