Max Kalehoff has a point here:
Today, mass-marketed Lego sets seem less about invention. They have become sophisticated model and hobby sets (often co-opting blockbuster entertainment franchises). Lego blocks are less raw building blocks, and more intricate puzzles with definitive outcomes. The highly specialized pieces are perfect for planned models, though I believe their lack of interchangeability across sets discourages invention. My kids seek to stay within the lines and preserve their models indefinitely, and these delicate things, while impressive, clutter our modest home.
That being said, I don’t think that’s a 100% truism all the time. Lego kits in my house have been built, admired on a shelf, taken off and played with like they were more sturdy toys, taken apart and had their parts used to build custom vehicles, buildings and more. So while yes, the intent seems to be more structured – I’ve even seen recent commercials where they’re played with in action – there’s still an awful lot of potential for kids to do whatever they want with the component bricks.