The main reason you cannot has to do with how browser handle these files.
- To retrieve style sheets, the html tag is
<link>
- To retrieve scripts, the html tag is
<script>
The html tag tells the browser what the contents of the file is.
On the MVC server side code, the main reason to use bundling is to combine script and link files into a single file. Then to minimize them. Bundling uses different minimization functions based on type of file. If you combine scripts and css into a single file, the bundling code will not properly minimize the resulting file.