Why do people love dark mode ?

A lot of my friends on Instagram use it my wife uses it from sunset to sunrise I can't handle it. Not sure if it's because I'm not use to it or what especially during the day with the sun shining on the phone it hurts my eyes I can barely see the screen. I can't get it on some apps like Google , Snapchat and Tik Tok. What's the big deal with dark mode especially in teenagers ? How do people use it during the day ?