I believe it's much to do with blue light emitted by screens:

https://pmc.ncbi.nlm.nih.gov/articles/PMC9424753/

For me most things I do on a screen are fairly mentally stimulating (like video games), and even the ones that aren't (like watching a movie) inhibit the feeling of sleepiness I get when I abstain. So, it's better for falling asleep quickly.