Yes, I know that, and am doing it, too, on my sites. Still, squeezing everything into a single HTML page, then applying CSS (and JS) fu to arbitrarily rearrange, add and drop content doesn't seem rational when website design processes draw upfront desktop, mobile, etc. breakpoints and sketches. Rather, CSS complexity seems a manifestation of organizational boundaries (eg. W3C specifying CSS and WHATWG specifying HTML) to me. Or even a post facto rationalization of the road not taken with HTML. Eg. almost all responsive designs used today can be achieved much more easily using adaptive techniques where there is a device/breakpoint-specific page layout for desktop, mobile, and maybe tablet, resp., with the page template documents pulling in content wherever it fits. It's just that HTML lacks mechanisms for page composition such as SGML's and XML's entity references. Arguably, responsive grids are not only more complex than needed, they're also inefficient wrt. network utilization, as every device has to receive every bit of content, just to hide it away when it doesn't fit the layout. Of course, large sites use JavaScript and visibility events to pull content on-demand anyway.
I'm not pissing on W3C's (fantasai et al) work here. CSS is very much a work in progress as we all discover new UI idioms for digital media, and I'm a sucker for it. I just think CSS grids and flexbox is bordering on intellectual brain wankery, when the solution could be achieved much, much simpler, and in a way that doesn't send newbies into a world of cluelessness, doesn't question our ability to consume our own digital media in the future due to over-complexity, and retains the qualities of the web as a medium for simple self-publishing even for a layman.
I'm not pissing on W3C's (fantasai et al) work here. CSS is very much a work in progress as we all discover new UI idioms for digital media, and I'm a sucker for it. I just think CSS grids and flexbox is bordering on intellectual brain wankery, when the solution could be achieved much, much simpler, and in a way that doesn't send newbies into a world of cluelessness, doesn't question our ability to consume our own digital media in the future due to over-complexity, and retains the qualities of the web as a medium for simple self-publishing even for a layman.