but it very often is. If you're a web developer, for example, little matters more to your users than performance. This has been demonstrated an almost infinite number of times by now, but surprisingly few industry professionals seem to pay any attention to it

Yes, and we can point that out to our business owners until we're blue in the face, but until they see the benefit they won't pay us to do that work. It can be surprisingly difficult to get this point across.

Just because something matters objectively, doesn't mean it matters to the client/business (at the moment). And unless you as the developer are in the position to dictate that, sometimes you're at the mercy of non-technical requirements or demands. You can be right about everything, but unless you're the boss, at least sometimes you can only do what you're told.

Little matters more to your users than performance, specifically, only features and security matter more than performance :)

And that the software is available (ie actually shipped). And to use it they need to know it exists and what it's for, which usually involves some marketing.