It's designed to be addictive. Every time you say to yourself "heh, what's one more 12 seconds video really?", it wins. It's the same as those games with microtransactions. Some people go a few times a day "heh, what's 0.5 bucks really?" without realizing that it adds up to 5-10$ a day, hundreds a month.
We live in an entertainment industry that gauges itself on "time people spend on MY platform". More time on theirs is more investors interested, and more of your habits sold to be fed on probabilistic machines to tailor adds to you.
If you are not sensitive to advertisement, it ain't a problem really. If you don't sacrifice a few times a day a good interaction for two or three videos, it ain't a problem. But if it starts impacting how available you are to the ones you love, it's starting to touch on the "addiction" official definition, in the problematic sense.