When President Calderon started the "war against drugs", it was not becuase he wanted to stop drug cartels, but because he tought that it would be an easy way to legalize his goverment... today there still there is a lot of people that think his party stole the elections..
So he started without any particular plan ...
Now, drug cartels know they are better armed that the mexican army (the probably have four or five more fire power in small and medium size arms), and know the power of money and terror.
The truth is that the only way to stop them, is somthing the goverment would not dare to do... supervise the financial system, where the money is cleaned...
That money... goes very high in the goverment... and the poilitical parties.. so nobody want it to stop...