As someone with young kids who recently bought a $70 Lego set, it’s not just the plastic blocks, it’s a whole design. My daughter built this awesome Lego tree house with over a thousand pieces. She followed the instructions and built it step by step over a few days, which was fun for her in and of itself, and now that it is complete she continues to play with it.

So sure the plastic pieces are easily reproduced but clearly Lego does great work on architecting some really cool designs. (I have no affiliation with Lego company to be clear)