Terraforming Mars

There has been quite a bit of discussion about terraforming Mars. While I do think it is possible my guess is that the process could take hundreds of years. Assuming that ET has been visiting us thousands of years (Ancient Astronaut Theory) why have they not already done this? They are far advanced technologically and likely have better and faster methods.

It puzzles me that we think we would do a better job maintaining Mars (after terraforming) than we have our planet. We have successfully overpopulated Earth beyond resource sustainability and are enroute to destroying the environment. Mars is not the solution.