For a long steeping tea, I can understand the string.
For one you're going to be whipping out after a few minutes, I like the tagless ones.
It means I can just throw them in, instead of fiddling wrapping the string around.
Don't you need to do this anyway even if it has a string, as you'll need to squeeze the bag at the top of the mug to prevent unwanted drips. Chances are you're making a cup of tea in a kitchen and a teaspoon will be within arms reach.
Going to go out on a limb and say continental Europeans tend to drink tea without milk so don't need to use a spoon, that makes having string more important