https://en.wikipedia.org/wiki/Eye_shadow

Eye shadow (or eyeshadow) is a cosmetic applied primarily to the eyelids to attract attention to the wearer's eyes, making them stand out or look more attractive.[1]

Eye shadow can add depth and dimension to one's eyes, complement one's eye color, make one's eyes appear larger, or simply draw attention to the eyes.

I just do it subtle with neutral colors. It’s like art. There’s some shading involved. It makes your eyes pop. Looks attractive:)

lots of reasons, but if the colors are bright or flashy or very noticeable, it's probably for fun.

Self expression

Because sometimes I like my eyelids to match my outfit or jewelry. Makeup is just like any other fashion accessory. I rarely do my makeup anymore, but sometimes it’s just fun.

And I wish more guys would join in. A guy wearing eyeliner is hot!

One of my kids used to do "nose shadow" instead of eyeshadow when she was little, would take my eyeshadow and paint her nose.

I don't makeup anymore (except for costumes) but it's for fun and to decorate yourself. Eyes are a logical part of the face to highlight.

I color the skin around my eyes to look younger and prettier! It works :)

Hopefully only because it helps their self esteem. But really, beauty standards, from marketing and peer pressure. It's not the worst thing to do, compared to some other trending ones it looks better to me and isn't as dangerous and permanent. That's just my own preferences though, I find minor subtle enhancements, if any more attractive.