- every time it was attempted, the generated html/css was terrible (think old ASP Net for example), and maintenance hard. Abstractions only work when they are not leaky
- designers, devs and users in general expect to have custom design for everything, rather than standard controls. Something to do with “have a unique brand and not look like everyone’s else app”.
We've come a long way in tooling, libraries, and in the underlying standards. Technologies like ASP also pre-dated SPAs and were targeted for server-side development; hence make for a poor analogy. Swing would be a more apt comparison, and even Visual Basic.
In general, poor execution in the past is no reason to drop the objective. We've tolerated plenty of bad HTML-based frameworks and years of CSS-quirkiness, yet we keep plugging away at it.
>and maintenance hard
But the actual objective is that you wouldn't hand-maintain the generated code. We're currently so bound to HTML-thinking that it's hard to embrace that notion.
>designers, devs and users in general expect to have custom design for everything
I've heard this. Interestingly, though, we look to tools like Bootstrap and design-motifs like Material, etc., which emphasize uniformity. Also, there's no reason branding can't be applied without directly manipulated CSS. A good component-based library would allow for that and would also allow for the construction of extensible custom components.