Frameworks are not bloated

[tkrotoff]

Bootstrap[...]
these frameworks can add unnecessary bloat to an experience [...]
users still have to download the framework’s unused CSS and JavaScript, resulting in slower page loads and frustration.

This is incorrect.

Bootstrap allows you to import only what you need.

https://getbootstrap.com/docs/5.3/customize/optimize/

Lean Sass imports [...] make sure you optimize Bootstrap by only @importing the components you need.

Lean JavaScript [...] This way, you’re not including any JavaScript you don’t intend to use for components like buttons, carousels, and tooltips.

In addition to only import what you need you can use the widely popular tool PurgeCSS. Bootstrap documentation also mentions it.

Is this a new feature and your book out of date?

No.
Example with Bootstrap v2.0.0 which was released in Jan 2012 almost 3 years before your book first commit in dec 2014:

• https://github.com/twbs/bootstrap/blob/v2.0.0/less/bootstrap.less
• JS plugins can be included individually, or all at once