Hello Cesar,
Firs of all what are your server and site settings? There are many tools to check it. If you have www and non-www you have duplicate content and probably thats why you lost on rankings.
For all my sites I used without www address and redirect everything *.example.com (all subdomains) to example.com (respectively http://www.example.com or http://example.com).
Why ... theory is internet behavior.
1. It's obvious that in present times more people search directly writing a words to search engine address field rather than write in google search-box field. So if you have a good brand it is more likely that they write your branded name than your branded name with the www in front of branded name.
2. www is a subdomain of a main domain - there's no point to guide people to subdomain.
3. In server configuration *.example.com with everything in subdomain will direct traffic to example.com
4. It is simple and short, now everything going to shortage and simplicity, why not site names?
5. Like in point 1 but bit different - it's mostly young users behavior to shortage addresses so treat 5 as a reaffirmation of 1 dedicated to the future 
It is my theory. Maybe someone will add something ...
Marek