As cm3 notes,
usability is as much if not more a concern than
privacy and
security. Though I'd not dislodge any of these three from a position of high primacy.
There's a risk / frequency trade off with all of these. Privacy can be quite possibly costly or fatal, though slightly more rare. Not so rare though that 20% of all Web users in a US Department of Commerce survey (see my recent comments history) report known credit card fraud. That's many tens of millions of affected users.
The security risks are similar but also extend to organisations which might stand to lose control over their own (validly) private information, or control over systems (see for example concerns over SCADA infrastructure, or industrial process control).
Usability and adaptability issues pose lower risks, but have a much larger affected field.
It goes well beyond the visually disabled, illiterate, and cognitively challenged. Anyone who's landed on a desktop site that's unusable on mobile has encountered a usability challenge. Google, Apple, Facebook, and Amazon are all rapidly pushing us, some kicking and screaming (I include myself) to an audible Web -- one in which the primary control and response interfaces are spoken.
What landing on a small set of templates does is provide for clearly parseable and understandable content. In a world where the goal isn't to read a full page but to extract and convey a useful item of information from it, wading verbally through megabytes of unparsable and nonexcludable content isn't particularly useful (and yes, figuring out how much a data reference is worth to the data-rerference intermediary is another question worth considering).
More generally, in my case, with only modest perceptual impairments (reading small, low-contrast type is among the earlier signs of your impending death), I've come to conclude for some years now that Web design isn't the solution, Web design is the problem. There are only so many ways you can present content that doesn't fuck with readability. I try, very hard, to ensure I'm not doing this on my own modest designs (look up "Edward Morbius's Motherfucking Web Page", a riff on a popular refrain, for my own principals in action).
My most common response when landing on a website is to sigh, roll my eyes, and dump it to something more readable. Firefox's Reader Mode. Pocket. Straight ASCII text. w3m.
And no, "novel graphic design" isn't conveying vast new amounts of information. I grew tired of hearing that argument 30 years ago, it's not got fresher since. Bloomberg, The New York Times, and the BBD are all experimenting with high-concept article formatting. In my experienct, without exception, it simply Gets In The Fucking Way.
My half-serious response to this is to create a new web browser embodying these and a few other principles. The working title is "the fuck your web design browser". FYWD for short.
Ninnies may opt to call it the Fine Young Western Dinosaurs browser as an alternative.