How to DRY when building back and front-ends?

Hello,

Since I'm new to MVC world, I'm spending a lot of time studying CI and looking at other's people code. One thing I noticed is that for some projects that have an "admin" and "front" part, there are a lot of repetition. Example: I'm studying a CMS code right now that duplicate a lot of files and coding. See for example how this CMS organised their template folder:

/template
    /back
        /js
            /jquery-2.x
            /jquery-ui
       /css
            /bootstrap
            /jquery-ui
    /front
        /js
            /jquery-2.x
            /jquery-ui
       /css
            /bootstrap
            /jquery-ui

They have exactly the same files in both back and front folders. I see that both back and front parts share the same foundation(bootstrap and jquery files). 

So, my question is, what is the best practice to avoid the repetition/duplication above?

Cheers,
Castle