Why do people watch music videos?

People who listen to music do it for a specific developmental goal: to define themselves and their tribal allegiances, and to learn about the tribal allegiances of others. This is why their hair splitting arguments about the difference between two similar-sounding genres carry so much heat -- it's not about classifying the music, it's about classifying themselves. The visuals add a lot of valuable social context to the music. You can see what the artists look like, their age and race and class, how they dress, how and if they dance, what instruments they show themselves using, what kind of physical settings they inhabit. If the videos are stylized and fantastic, there's still plenty of information there; it's just more emotional and symbolic. 

Kids exclusively watch on the computer, or on their phones. The sharing and discussion of the videos is as important as the videos themselves, thus the appeal of YouTube and its easy integration with Facebook, Tumblr, and Twitter etc.

As a child video chart shows were a staple of my weekly viewing, and even in uni flats it was super common to have a music video channel on most of the time. They hardly played music we actually strongly liked either, there was virtually no alt stuff on, just a mix of top 40 pop and classic oldies/rock.

In theory music video creation must be burgeoning with the relative inexpensiveness of digital video cameras and editing software (and platforms like YouTube, at least at the DIY level.)

I occasionally watch a video and enjoy it, but a lot of the time I just find my attention wavering and I want to listen to the song but do something else with my eyes. Partly because the videos are often dull and unimaginative

Probably more interesting is live footage, or like black cab style alternate / in the radio studio versions of songs. Which is something, but is of course different from the seemingly moribund art form of the music video?