Given the phrasing, the answer is: marketing! But the answer I suspect you're looking for is a little more nuanced. These days, when LEGO makes a set, they start with a target audience. read more
LEGO does a lot of testing to determine which age ranges of kids can reliably do things at what ages, both with and without previous LEGO building experience. Sometimes, LEGO actually makes special elements that are intended to make this easier. read more
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