Actually, the vast majority of children report that their parents set no limits on screen time. I could dig up this reference for you if I had the time, but I recently read a big long academic article about this.
Also, the average kid between 7 and 18 spends 7 hours per day on screen time. This does include simultaneous screen use (counts it "twice").
So...it's a lot. I'm not opposed to this in a blanket sense, but I do also feel a bit cringey when I see it. We were on vacation recently, eating outdoors in a really stunningly gorgeous spot overlooking the ocean, and the family at the next table over had two teens completely absorbed in screens the whole time.