A lot of Noctua sales come from their brand value. People put Noctua fans into their gaming PC's, use headphones while gaming on them, and then turn off the PC. You don't really need the most silent fan for that, but people buy them anyway for the looks & premium quality.
I do love Noctua's coolers though, I appreciate the well thought design, manuals and free upgrade kits when you upgrade your system to a new socket type. But for case fans I'll jut buy Arctic and save money, except for things like server systems that run 24/7 in my bedroom where noise and durability are top priority.
... which is why I only have a few of them, rather than replacing the fans in everything I own. But for the things that need them, there's just nothing else as good.
This is an enthusiast product, as evidenced by the premise that you care about color-coordinating the inside of your computer.