Why is there so many drug cartels in Mexico?

It has a weak government (huge sections of the country are essentially "no go's" to police, where the cartels are in complete control, and it's the central hub between the supply (central/south America) and the demand (north America).

There are so many poor people the government lets the drug dealer make a little money too.

BIG MONEY and a weak government ....................

Because the buyers are in the US. There used to be more drug cartels in Colombia, but the government there, with the help of the US, cracked down on them, so they moved to Mexico, where it's easier to get drugs across the border to the US. If people in the US STOPPED BUYING DRUGS, the cartels would quickly die out. 

lets put it this way ..if mexico was where alaska is then it would not be a problem .....but its location and climate  

Pure and simple, the demand for drugs creates a huge profit for anyone able to supply them. The socio-economics of countries such as Mexico make for an ideal place to produce and distribute large amounts of illicit drugs. It comes down to supply and demand however. If you can manufacture something for $1 and sell it for $100, someone somewhere is going to do so.

Maybe because there is a lot of drugs in Mexico.