[matt4077]

What changed are browsers. The original advantage of bootstrap et al where grids and standardisation. These initial use cases have been subsumed by browsers, and bootstrap offers little more than a useless level of redirection.

Then, bootstrap added what I want to call widgets: small functional units that can easily be reused. Here, as well, browsers have changed dramatically. At the time bootstrap came out, these widgets required browser-specific, inscrutable hacks like negative margins, spacer pixels, and other crimes against htmlanity. Relative to 10 years ago, all of today's browser engines are identical, and CSS has added all these typical use cases.

What remains is more or less a skin changing html's defaults to something that may be prettier, or just not weighed down by the stigma of being the default.