Source Maps Not Generated by WebPack

Admittedly, I have basic understanding of source maps and webpack. It is my understanding that if I set the devtools correctly in my webpack.config.js file, I should get source map files that map to original code.

I'm using the following config file and I'm not getting any source map files. Any idea why?

var IS_DEV = false;

var webpack = require('webpack');
var path = require("path");

// Define plugins needed for production and dev cases
var _pluginsDev = [
    new webpack.ProvidePlugin({
        'fetch': 'imports-loader?this=>global!exports-loader?global.fetch!whatwg-fetch',
        moment: 'moment',
        ps: 'perfect-scrollbar'
    }),

];
var _pluginsProd = [
    new webpack.ProvidePlugin({
        'fetch': 'imports-loader?this=>global!exports-loader?global.fetch!whatwg-fetch',
        moment: 'moment',
        ps: 'perfect-scrollbar'
    }),
    new webpack.DefinePlugin({
        'process.env': {
            'NODE_ENV': JSON.stringify('production')
        }
    }),
    new webpack.optimize.UglifyJsPlugin({
        minimize: true,
        compress: true,
        output: { comments: false }
    })
];

var _devtool = IS_DEV ? 'eval' : 'cheap-module-source-map';
var _plugins = IS_DEV ? _pluginsDev : _pluginsProd;
var _fileName = IS_DEV ? "./build/[name]-bundle.js" : "./dist/[name]-bundle.js";

var _bundles = {
    login: './components/login/login.jsx',
    home: './components/home/home.jsx'
};

module.exports = {
    entry: _bundles,
    output: {
        path: path.resolve(__dirname, "wwwroot"),
        publicPath: "/",
        filename: _fileName
    },
    devtool: _devtool,
    plugins: _plugins,
    module: {
        rules: [
            {
                test: /\.jsx?$/,
                exclude: /(node_modules|bower_components)/,
                use: {
                    loader: "babel-loader",
                    options: {
                        presets: ['es2015', 'stage-2', 'stage-0', 'react']
                    }
                }
            }
        ]
    },
    resolve: {
        extensions: ['.js', '.jsx']
    }
}