promises isn't a magic tool, or simply - they don't work

promises-dosnt-work.js

var fs = require('vow-fs'),
    vow = require('vow');

/**
 * @param {String} path
 * @returns {Promise} representing css
 */
module.exports = function processNode(path) {
    return fs.isDir(path)
        .then(function(isDir) {
            if (isDir) {
                return fs.listDir(path)
                    .then(function(list) {
                        return vow.all(list.map(function(node) {
                            return processNode([ path, node ].join('/'));
                        }));
                    })
                    .then(function(data) {
                        return data
                            .filter(function(item) {
                                return item;
                            })
                            .join('\n');
                    });
            } else if (/\.css$/.test(path)) {
                return fs.read(path).then(function(data) {
                    return [
                        '/* ' + path + ': begin */',
                        data.toString()
                    ].join('\n');
                });
            }
        });
};