I've used bootstrap many many times in my line of work: internal tools and systems for corporate use. I'm not a web designer, neither a full time web developer, so it's really really nice to have a drop-in barebones decent looking and well though interface to work with.
I'm not a big fan of bootstrap but it does a heck of a lot more than just grid layouts. You can't just easily replace the components (modals, accordions, buttons, etc) with CSS grid.
It is not just `display: grid` that is replacing the layout. Now we also have interactive elements in the HTML spec[1] like `<dialog>` and `<details>`. We also have custom elements making an all in solution like bootstrap less desirable for everything except quick prototyping.
So, where's the equivalent one stop shop for someone building an admin interface using these new features? Don't think uber.com - think admin.startup.com .
(Personally, I'd rather they just build it in Lazarus, but people have forgotten about building desktop apps.)
Dialog is nice if you only support Chrome and Firefox. Maybe when Edge turns to Chromium it won't be as bad, but the truth is that Bootstrap is accessible in most if not all modern browsers, but the new HTML5 elements are not.
You can always drop in a polyfill[1], and when browser support picks up, you can remove it from your dependencies. That is what people used to do when they decided to omit jquery in favor of native web APIs a few years back.
Right - so you get all the functionality of bootstrap using CSS grid; all the modals, spinners, buttons, and most importantly: browser bug fixes and quirks people contribute over time.
Bootstrap is a _framework_, not just a layout system.
Also, BS uses Flexbox at the moment, I doubt they'll go to grid any time soon.