SCSS file is exported into build folder. Plugin-sass

[rokobuljan]

I have: inside /src/css/ two SCSS files: _app.scss and index.scss which just uses @import "./app";
I'm using the plugin-sass

    plugins: [
        ["@snowpack/plugin-sass"]
    ],

and by running build , inside the /build/css/ folder I get index.css (which is minified and works just fine!)
but there's also the teleported _app.scss.
Cannot understand why this is happening. I find pretty silly the need to add into snowpack.config.js something like exclude: ["**/_*.scss"], for it to work as expected. Why would anyone want .scss files inside the /build/css?
Is there something I'm missing?

Current config:

module.exports = {
    exclude: ["**/_*.scss"],        // why ???
    mount: {
        public: "/",
        src: "/"
    },
    plugins: [
        "@snowpack/plugin-sass"
    ],
    packageOptions: {},
    devOptions: {},
    buildOptions: {},
    optimize: {
        bundle: true,
        minify: true,
        target: "es2018"
    }
};