I would agree that what you state are factors, but I would disagree that they are the main factors.

One thing I notice in my work (in product management) is that people naturally gravitate towards shiny things. So we design things to be shiny in order to attract those people.

At various points, a specific aesthetic gains popularity because, for well-founded reasons, it increases usability and readability. Then everyone starts to imitate it, partly because it works, but also partly because people are drawn to it. Then frameworks are created to enable teams to rapidly replicate the style.

At a certain point, the frameworks are good enough to just replicate the style in basic settings with little input needed from someone who is actually thinking really hard about the design. In many ways that's a good thing because it lowers the barrier to entry. It's much easier to make things because the framework drastically reduces the amount of wheel reinventing you'd need to do. But you end up with designs where nobody really thought that hard about it - and so you end up proliferating potentially bad defaults encoded in the frameworks.

I'm personally much more willing to believe that the decline in overall design quality is due to negligence from convenience.

I think you're conflating design and engineering.

It's rarely the case that you change design because you selected a new technology; rather you usually select a new technology to enable changes in design.

If I switched from React to Vue for a Hacker News viewer I'm not also going to change the design of the project just because. But if I wanted a dashboard to become dynamic and allow for smoother user experiences without a full page refresh each time chances are I'm going to introduce JavaScript to a page that was previously just HTML and CSS.

Nah, the core problem on is the misuse of opacity, too many shades of one color (such as the light gray in the article) instead of relying on weight variation, dividers, italics, etc.

Take this block of text in the article:

"I thought my eyesight was beginning to go. It turns out, I’m suffering from design."

Instead of leaving it a legible black and have the divider + italics convey the separation from the article...

They went with rgba(0,0,0,0.5) on a font that is hard to read on a white background with that shade of a gray. Try removing those sort of CSS rules from the Wired Article and you'll find it much more legible.

They repeat this sin whenever they quote someone such as:

A color is a color isn’t a color… …not to computers…and not to the human eye.

They also put a ton of whitespace around the quote which is already enough to separate it. The absurdly annoying light gray is annoying and not required.

There are also many sites that are highly successful and use 2MB of javascript. I'm not sure what this proves, except that when an app is useful users won't be put off by the technology or even user experience.