Why doesn't the style.scss file compile normally to style.css?

Question

WordPress

In the main style.scss file, everything is fine with @imports, if so.
Structure:

var   themename = 'mytheme';

var  gulp               = require('gulp'),
       plugins          = require('gulp-load-plugins')(),
       image            = require('gulp-image'),
       sass               = require('gulp-sass'),
       cleanCSS       = require('gulp-clean-css'),
       browserSync  = require('browser-sync').create(),
       sourcemaps   = require('gulp-sourcemaps'),

    // works with new or updated files
    newer = require('gulp-newer'),
    
    // Name of working theme folder
  root = '../' + themename + '/',
  scss = root + 'sass/',
  js = root + 'js/',
  img = root + 'images/',
  languages = root + 'languages/';

// CSS via Sass and Autoprefixer+CleanCss
gulp.task('buildcss', function() {
    return gulp.src(scss + '{style.scss}')
    .pipe(sourcemaps.init())
  .pipe(sass({
    outputStyle: 'expanded', 
    indentType: 'tab',
    indentWidth: '1'
    }).on('error', sass.logError))
    .pipe(plugins.autoprefixer(
        ['last 3 versions', 'ie 11']
    ))
    .pipe(cleanCSS())
    .pipe(sourcemaps.write(scss + 'maps'))
  .pipe(gulp.dest(root));
});

// Optimize images through gulp-image
gulp.task('images', function() {
  return gulp.src(img + 'RAW/**/*.{jpg,JPG,png}')
  .pipe(newer(img))
  .pipe(image())
  .pipe(gulp.dest(img));
});

//Watch
gulp.task('watch', function () {
    browserSync.init({
        proxy:'merchant',
        notify: false
    });
    //Watch css and .scss files
    gulp.watch([root + '**/*.css', root + '**/*.scss' ], ['buildcss']);
    gulp.watch(js + '**/*.js', ['javascript']);
  gulp.watch(img + 'RAW/**/*.{jpg,JPG,png}', ['images']);
  gulp.watch(root + '**/*').on('change', browserSync.reload);
});

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

Answer 1

Why are curly braces here?
return gulp.src(scss + '{style.scss}')