Creating a UI component library is a common practice nowadays. There are many good examples out there, being bootstrap and foundation some of the most popular as of this writing. Although those are good options for prototyping, there are some reasons while they might not work for big companies.
They need customization to match your company image; If you want to use them for your company you might end up tweaking it so much that it no longer look like the original library.
They are bloated; They are made to meet multiple needs so they include many components that you might not need. Even when you can create your custom build, the components themselves are made for flexibility so they will most likely include stuff you don’t need too.
They are not components; These libraries call themselves UI frameworks, so they are not really component libraries. They usually provide a plethora of useful classes that you can incorporate into your HTML, but there is no really way to say “I want this thing in my page”. You have to do it yourself. Some components they offer also need JavaScript, which means that to use the framework you need to include the CSS and JS and then add the correct classes to your HTML. In a lot of scenarios this is acceptable, but probably hard to scale.