I think the technology also dictated it. It’s easy to forget that in those days the idea of window chrome being full color, full transparency, with live window dragging and visuals not locked to tiling 8x8 or at best 32x32 elements was incredibly novel. And that was as much about preemptive multitasking and expecting and allowing every application to keep its windows up to date as it was about Quartz.

Aqua was garish and in your face, but it needed to be in order to be a symbol of what the system had achieved, which I think was especially important because that came at the cost of being a buggy, immature OS that had to run crucial apps in a hideous compatibility mode while it was getting established.

Edit: and if I can be a cranky old codger for a moment, I think that Liquid Glass unintentionally serves just as well as a symbol for what Apple has become: a company grasping to relive the memory of innovation without remembering how to innovate.

At the time there was also a major push to bring desktop computing and the web to the general population, remember this was a time when cutting costs enough to market a $1000 PC ($2000 adjusted for inflation) was considered a major achievement, the very bottom of the market. I get the sense that Apple was trying to distance its design as much as possible from square-cornered beige boxes as possible to signal that the products were for normal people.