I'm currently writing a toy "javascript" bundler. I implemented a CSS parser in the past (mostly for linting) and it took me a few hours. Trying to do the same with SCSS made me give up halfway. The test suite was >6000 tests or so and I got up to about 3000 or something, but it gets harder the further up you go. There's lots of other people in Github that are smarter than me and had the same experience, leaving their parser halfway finished. There's a lot of smart stuff in SCSS, and that is perfectly fine for a compile-time tool, but it's not something that's fast enough for a browser, or simple enough that can be added quickly to their current parsers.
I'm currently writing a toy "javascript" bundler. I implemented a CSS parser in the past (mostly for linting) and it took me a few hours. Trying to do the same with SCSS made me give up halfway. The test suite was >6000 tests or so and I got up to about 3000 or something, but it gets harder the further up you go. There's lots of other people in Github that are smarter than me and had the same experience, leaving their parser halfway finished. There's a lot of smart stuff in SCSS, and that is perfectly fine for a compile-time tool, but it's not something that's fast enough for a browser, or simple enough that can be added quickly to their current parsers.