The problem is the perception by many that this is a kids toy. I have a 5 year old daughter, so even that excuse barely works :D
It's insane to consider how massive Lego has become. In my mind, the 1980s are still the golden age of Lego: every set was iconic, at least in my mind. Many of the current themes were started in the early 1980s. At some point, ver a decade ago, I feared they'd lost their way and making sets of questionable design that seemed to have forgotten what Lego was about, but now they're back. They're just doing everything: the Creator line that's about building stuff, the City line has more than just police and firefighters now, there's a new, more realistic space line (part of City actually), the different look of the friends line, but also (finally!) more female minifigs in other lines. There's tons of licenses, collectibles, programmable Lego of several kinds, mobile games, the cool stuff coming from Ideas, etc. The only thing I kinda miss is their Lego boardgame line. But other than that, it seems they're hitting every market at once, from every possible angle, and they're surprisingly effective at it. I think they surpassed Hasbro as the largest toy maker in the world, didn't they?
Those sets have larger parts and can be build within the attention span of a child. And they are mostly something hands on like cars or planes that the kids like to play with.
Then even larger sets can be cool for children. I just bought and build the current moon station but that turned out to be not as good looking as I imagined. But my daughters (4 and 6) immediately took control of it. Especially the pizza dispenser was a highlight for them.