The technology/internet makes things more complex, makes the mind more active. Youtube, Facebook, Twitter other social media platforms or other internet sites etc.(and now with digital things people is able to engage in these things all the time because internet is not only in computers but now it is in people's "hands" all the time). One thing after another arises in the mind and people identify with everything that arises in their minds.
So people are in the mode of "This is important, another evil coming in!".."A text message..It must be important".."Somebody just posted something in facebook"..And the attention is completely absorbed by these things. It was bad already before the digital things but now it is amplified. It causes more stuff in the mind. One thought after another, one text message after another, one facebook post after another, one unpleasant memory or anxious thought after another. And imagine living like that for 10, 20, 30, 40 years. What kind of "person" would that life-style and mind state produce? Angry or anxious..Continuously dissatisfied..Continuously needing desperately the next thing. And life becomes permanently "never enough".
And it is same for the music as well. In the cafes they generaly play the same songs that becomes famous in the last times. I heard a song recently in a cafe that had this words: "I would not stop the blood that would shed for the sake of you". And I opened the youtube clip of the song and I saw that the singer is smiling with deep "joy" while saying these words. And I read the comments under that video-clip and countless of people wrote(and ofcourse still writing) praising, glorifying things about the singer and the song.
To give another example of the internet's effect on the human mind: I saw that an important character in another internet platform(And that person is the "idol", "guide", "teacher", "leader" admirable person for that group of people) had a picture that gives the message of glorifying and advocating killing. The picture is no longer on that profile(in my computer I can't see a picture in that profile anymore) but we all know that these things exist in all of the internet world.
That's the reason why watching youtube, social media and many other things in internet makes people more absorbed than simple reading of harmless things.
The Buddhist path leads it's followers to realize that humans are not the reference point. Most areas of internet leads people to the opposite direction. While accepting and realizing this (humans are not the reference point) is the hardest thing for the meditators(but it is necessary to find permanent peace and freedom), it is not a useful thing to engage in internet too much. One of the best solution for these things is to have a sangha(living or spending a lot of time with meditators). As Thich Nhat Hanh said:"Don't be a drop of water". In many places of the world this is hard but in Western and Buddhist countries plus Australia this is possible. With having a Sangha a person can more easily save the mind from these things or at least diminish the time that s/he spends in the craziness of the internet world.
And yes it is about lack of mindfulness but internet world naturally leads people to unmindful state. So the solution is try to be mindful while spending the time internet and gradually spend less time. So the mindfulness would not diminish and replaced by the internet world's effects.