When connecting Bootstrap-SASS and minifying it through GULP, the output file increases by 2 times compared to CSS from offsite?

Question

Sass

I assembled a blank for quick layout of projects using NMP,
Bootstrap-SASS as the basis for layout,
GULP for automation and minification, since I had not worked with it before, I took this article from Habrahabr
gulpfile.js as a basis:

'use strict';

var gulp = require('gulp'),
    watch = require('gulp-watch'),
    prefixer = require('gulp-autoprefixer'),
    uglify = require('gulp-uglify'),
    sass = require('gulp-sass'),
    sourcemaps = require('gulp-sourcemaps'),
    rigger = require('gulp-rigger'),
    cssmin = require('gulp-minify-css'),
    inject = require('gulp-inject'),
    imagemin = require('gulp-imagemin'),
    pngquant = require('imagemin-pngquant'),
    rimraf = require('rimraf'),
    browserSync = require("browser-sync"),
    reload = browserSync.reload;

var path = {
    build: {
        html: 'build/',
        js: 'build/js/',
        css: 'build/css/',
        img: 'build/img/',
        fonts: 'build/fonts/'
    },
    src: {
        html: 'src/*.html',
        js: 'src/js/main.js',
        style: 'src/style/main.sass',
        img: 'src/img/**/*.*',
        fonts: 'src/fonts/**/*.*'
    },
    watch: {
        html: 'src/**/*.html',
        js: 'src/js/**/*.js',
        style: 'src/style/**/*.sass',
        img: 'src/img/**/*.*',
        fonts: 'src/fonts/**/*.*'
    },
    clean: './build'
};


var config = {
    server: {
        baseDir: "./build"
    },
    tunnel: true,
    host: 'localhost',
    port: 9000,
    logPrefix: "Frontend"
};

gulp.task('webserver', function () {
    browserSync(config);
});

gulp.task('clean', function (cb) {
    rimraf(path.clean, cb);
});

gulp.task('html:build', function () {
    gulp.src(path.src.html) 
        .pipe(rigger())
        .pipe(gulp.dest(path.build.html))
        .pipe(reload({stream: true}));
});

gulp.task('js:build', function () {
    gulp.src(path.src.js) 
        .pipe(rigger()) 
        .pipe(sourcemaps.init()) 
        .pipe(uglify()) 
        .pipe(sourcemaps.write()) 
        .pipe(gulp.dest(path.build.js))
        .pipe(reload({stream: true}));
});

gulp.task('style:build', function () {
    gulp.src(path.src.style) 
        .pipe(sourcemaps.init())
        .pipe(sass({
            includePaths: ['src/style/'],
            outputStyle: 'compressed',
            sourceMap: true,
            errLogToConsole: true
        }))
        .pipe(prefixer())
        .pipe(cssmin())
        .pipe(sourcemaps.write())
        .pipe(gulp.dest(path.build.css))
        .pipe(reload({stream: true}));
});

gulp.task('image:build', function () {
    gulp.src(path.src.img) 
        .pipe(imagemin({
            progressive: true,
            svgoPlugins: [{removeViewBox: false}],
            use: [pngquant()],
            interlaced: true
        }))
        .pipe(gulp.dest(path.build.img))
        .pipe(reload({stream: true}));
});

gulp.task('fonts:build', function() {
    gulp.src(path.src.fonts)
        .pipe(gulp.dest(path.build.fonts))
});

gulp.task('build', [
    'html:build',
    'js:build',
    'style:build',
    'fonts:build',
    'image:build'
]);


gulp.task('watch', function(){
    watch([path.watch.html], function(event, cb) {
        gulp.start('html:build');
    });
    watch([path.watch.style], function(event, cb) {
        gulp.start('style:build');
    });
    watch([path.watch.js], function(event, cb) {
        gulp.start('js:build');
    });
    watch([path.watch.img], function(event, cb) {
        gulp.start('image:build');
    });
    watch([path.watch.fonts], function(event, cb) {
        gulp.start('fonts:build');
    });
});

gulp.task('sass', function () {
  return gulp.src('./sass/**/*.sass')
    .pipe(sass().on('error', sass.logError))
    .pipe(gulp.dest('./css'));
});

gulp.task('default', ['build', 'webserver', 'watch']);

Bootstrap-SASS included in main.sass

@import "../../node_modules/bootstrap-sass/assets/stylesheets/bootstrap"

As a result, the original bootstrap-a base files are 143 kb.
My output is 331 kb.

Answer 1

.pipe(sourcemaps.write())
You write the source map directly to the file. Of course the size will be huge.
Write at least so that the sourcemap is written to a separate file next to the css
.pipe(sourcemaps.write('.'))

Answer 2

Thank you after deducing the sourcemap into a separate file - 113 kb.