The first is that phones and light break our natural sleepiness triggers and the second is that we don't exercise our bodies enough because of our sedentary lifetstyle.
I used to struggle with terrible insomnia and I still get bouts of it time to time but I've also found it's related to my laxing my 3 rules.
If I have a good workout about 5x a week, I turn off my phone and the lights 30 minutes before bed and take a good long shower in the dark and I have a regular alarm set at 7am that goes off 7 days a week, I'm almost guaranteed a good nights sleep every night. It also had the added affect of ridding me of my night terrors and sleep walking I used to have frequently but I'm 90% certain that was correlated to me using my phone in bed and it causing my brain to enter a weird state where it never really turned off.