THE DUMMY SiTUATiON

I have been watching a woman with her 4 month old boy for a while now.
The wee one is really easy going, most of the time just lying around watching the world above him checking out his hands and tiny fingers. Every now and then he starts "talking", commenting on what he sees, then again just sucking on his hand. And this is where mommy comes back with her big hand putting the baby-soother in is mouth. He wasn't crying, certainly did not ask for it. But now he's got it, first he wonders and then obviously starts sucking a bit. A little later he's back on the talking, the dummy falls down. He doesn't even care, keeps talking. And yes... it won't take long and mommy is back with the soother.
WHY ???

I do kind of understand that parents get frustrated with their screaming kids, I see why they use the a soother to keep it quiet although I am not a big fan of stuffing your child's mouth. But why do it when the little one clearly does not even care about a soother, when it does nothing but talk to himself? How come that the soother has become such a necessity ?

I know, I'm still not in the situation to completely judge. But I am wondering. I for myself have decided to try it without, rather see my little one with the thumb in his mouth when he feels the need for it. Makes him less dependent on me picking up his soother all the time. Just to mention one great advantage.

But maybe parents have a very good reason? So far I have not heard a convincing one. Do you ?