I watched it happen as it happened when I was 13. I remember the immediate "fuck these assholes let's get em" response that followed. The years of bullshit political fuckery, oil and heroin trade wars, our economy being jewed to shit over this nonsense to the absolute state it is now. Growing up in a trad, neocon, household with people who were stuck in the 1960s about how the world worked at best during this time was hell incarnate. Hearing retards like Michael Savage and Limbaugh ad infinitum was torture. The entire 'murica meme was essentially spawned from the commercialized hyperpatriotism of the era. This country was so fucked in the ass that saying Bush was a retarded asswipe who destabilized the middle east for no reason other than to do so and outright AVOIDED confrontation with the country who effectively pulled this shit off was akin to high treason.
911 was so much worse of a shit show than a lot of people remember, not just because of the incident itself but the absolute social and political retardation that followed.
What I think happened is that the Saudis realized they could, through their enormously growing control over oil reserves and supply by beginning to use USD as the exclusive trading currency for such material, get the US by the balls politically and economically and bid their time for a decade. Hence why we ultimately wasted our time in Iraq and Afghanistan though gigantic swaths of evidence pointed elsewhere and the whole WMDs thing turned out to be a fat fucking nothingburger. They realized at some point our government was and is too fucking stupid and uncoordinated to really prevent such a thing (people really don't seem to remember how lax security was everywhere pre-911) and saw an opportunity. They hit the World Trade Center for fucks sake. What better target if you're going to pull some shady dealing like this that can affect WORLD TRADE, and want to not only cover all of your tracks, but also send a message and entirely confuse your target and obfuscate your interests at the same time. That's my dumbass take after two decades of being alive post this shit, and one decade prior of knowing what at least a somewhat peaceful world could've been like.