@bythewell - There are plenty of descriptive poems which are beautiful and as far from greeting card writing as can be.
Just because something is descriptive doesn't mean it can't also have a deeper meaning or be lovely for its own sake. I think people consider it to be dull because often it is undertaken as a dull exercise.
But if you were going to get students to do descriptive poetry for kids, you'd get them to describe things which are dear to them, or interesting to them. A vivid description of a cartoon, which describes not only the obvious things but the not so obvious, like the funny postures, but also the pixels and the blip in the center of the screen when the TV goes off.
Humans are always going to look for deeper meaning. If they don't, they will just see the nice description, if they do, they might see their own death in that blip.
I think descriptive poetry is just another way of getting things across. Perhaps it's too subtle for some.