Here the tendency started years ago because kindergarten children were allowed to make so much noise that they had to shout to each other to hear what was being said.
In the 1970s I noticed that we had to insist that the children spoke "in a normal voice" at home.
A great part of my time as a teacher from the 1980 until I retired in 2013 was spent asking children not to shout, but to talk at a reasonable level.
I noticed while we were travelling in Europe that in Germany, France and the Netherlands, but perhaps particularly in Germany, people in shops, restaurants or other public places still talk quietly to each other and rebuke their children if they speak too loudly.
I wish the same thing was still customary here. I suppose all we can do about it is to point out to those we know well enough that we are not deaf, so the don't need to shout.
One school child actually said to me, "You'll need to shout if you want us to hear you." My reply was that I had been brought up to consider it very rude to shout at people, and I would feel ridiculous shouting, "Be quiet, please!"