I see no reason for using a third party layout system now that CSS has `display: flex;` and `display: grid;`. As for modals and menus, HTML has `<dialog>` and `<details>`. And for reusable components, we have custom elements, that you can either implement your self (not that hard) or pull from a library (using javascript modules).
Really the only reason I see anyone using CSS frameworks like bootstrap is for quick prototyping or because that is what they know and don’t bother picking up the new standards (which is ironically where jquery was a few years ago).