It also means, for front-end developers like me, that I can create a company theme on Bootstrap, and get junior developers to use it can feel comfortable with being able to implement the brand design language and not have to pixel-fiddle. Not only does this strengthen the technical skillset of my team, but it also helps keep standards high when dealing with offshore resources.
We can get them to build UI for entirely separate projects, slap our branding on it, and dramatically cut down on resource allocation, time, and effort.
So, here's the thing: this is great, but Bootstrap also has utility classes these days. If I use Tailwind, or Foundation, or Bulma, I immediate lose out on developer leverage. This is so much more powerful than moving some classes around.
Approaching all of these design concerns in a slightly different way just isn't powerful enough to outweigh the leverage Bootstrap has over everything else out there.
It's just not significantly different enough. It doesn't standout to me. In fact, how it differentiates in its introduction is a _con_ to me. No, the industry doesn't need complete UI kits, design languages vary enough that this could provide additional undesired weight, however people use buttons, drop-downs, and many other common components _all the time_.
A major competitor to Bootstrap in the arena would need to do something revolutionary.