No one is born with an innate desire for that specific Barbie or Lego set. The companies market to you, make you feel like you want it. The companies may not be able to change the entire macro environment, but they actively profit and exploit it.
So yea, they are way more to blame than what 11 year old girls think their place in the world is. Who do you think told them?
True, but it's the fault of both companies and consumers at the same time. It's a feedback loop. Marketing strategies are based on what people are willing to buy, which is based on what companies market. The system feeds on itself.
That said- you can still buy all of the plain bricks you want from their website. If you don't want the complicated sets, don't buy them. The blocks on their own are fine.
If adverts have more of an influence on your kids than you do, then you're a terrible parent.
For the downvoter(s), a thought experiment: lynch mobs.