Modern CSS has _some_ of the features of SCSS/SASS. It does not have all of them. But most importantly, many of dependencies one might want to use also make use of SCSS/SASS downstream. If you're happy to build everything from scratch and eschew any dependencies that require a build system, then have fun explaining to your product person why it took so much time to build a thing that they know very well is a pre-built component in some frontend library somewhere.
> Modern CSS has _some_ of the features of SCSS/SASS. It does not have all of them
You say it like more those features are desirable.
> then have fun explaining to your product person why it took so much time to build a thing that they know very well is a pre-built component
Sure. I wasted more time getting an assortment of pre-built components to behave than I did building the basics from scratch. And then comes a breaking change. And then that component library uses styled components and doesn't run properly on the server. Why do people do this to themselves?