But today it seems that the purpose of most boxes is to do only that - and then, what, put the object into a display case? Or, more likely, play with it for a while and then forget about it.
What I mean is that even though today's lego boxes let you build way more realistic and designy products, there are so many special pieces that it does not spark your own creative fantasy (in my opinion) but limits it. To me, as a child, the appeal was always that there was quite a limited set of brick types - and the creativity lay in combining them in new ways.
In comparison, the number and types of different pieces seems to have doubled or tripled today. By implication that means that you end with a few instances of many different types of pieces while before, you'd have many instances of a few types of pieces. I'd argue that the latter lends itself much better to creating new things born out of your own creativity.