Isn't a 50/50 map essentially what a stock map is? I mean in terms of delivering balanced performance?
Sort of, but a standard map is designed to meet marketing requirements, poor maintanance, varying climates and fuel economy and local tax and insurance implications. There are other reasons I'm sure.
An eco map would boost torque mildly and you would drive it accordingly, boosting mpg. A performance map boosts torque and power by more and, if driven sensibly, will do the same as an eco map.
If I'm being cynical, i'd say that an eco map is a marketing gimmick to lure in those who aren't interested in modifying cars, although if insurance companies get on board with the idea, it could be a useful compromise for some.
If you hypermile any car, you can get high mpg. On a standard car you will be going very slowly, on a mapped car you can hypermile easier and travel faster whilst doing so.