There's thirteen of them.
On average, a music video is three and a half minutes long. That's 16.15 seconds of video each, if you split it up exact. That's also not including the full group shots (shots of them dancing, interacting, etc), and anything they want to put for filler, like if the video has a story. So let's cut that to half the video for group/duo/gathering/dancing/story shots. Each member now has 8 seconds of focus time each. 8 seconds. This should be acceptable, and you need to learn to expect only this much if you're into a group with so many god-damned members. Though, this also doesn't count the fluctuations in member popularity, which I'm sure has some influence on what members show up when.
Just shut up. Pick a new fandom if it makes you cry so much.