As a mexican I can tell you it's not so simple, first of all Mexico while still a third world country is not some poor helpless lost country. We have our own resources, we have our military, marine, air force, police forces etc. It's not that much an issue of resources, even if the U.S. would borrow their drones and made perfect drone bombings there are a lot of people waiting their turn to be the next kingpin. You kill one and then 10 guys show up to take their place since there is poverty in many parts of Mexico. Hell there is poverty even in many parts of U.S. (Detroit for example). So as long as there is demand for drugs there will always be people willing to sell it and be rich. Killing bad guys here is like trying to kill the hydra, plus we have a big problem with corruption so there are people in the government who don't really want the drug sale to end.

Also U.S. sending troops to our country is a big sovereignity issue, would you like a foreign nation sending military troops to your soil? We have a history of foreign interference and nobody here likes it, it's not ok.

There's also what spitfire8125 said, I can tell you from a "third person perspective" (not being an american) it's pretty obvious the USA doesn't go to distant lands to help people, they go for their own interest even if it's not obvious at first. This is a thing american people have a hard time accepting, your government is not a force of good trying to make things right in the world, it's a big resourceful entity trying to keep it's hegemony over the world. 99% of the time your government goes to another country is for two reasons: security (for USA) or resources.