"We can't tune your ecu" said tuners, why?

When I ask tuning shops if they could tune my Lancer EX 2012, they said that they can't tune my ecu. What is the reason that they can't tune my ecu? I thought ecu tuning can be done on all types of cars..

Maybe simply because they are not equipped for it.

Stock ECU? From a quick Google search, your car has a non turbo charged engine, these are a lot harder to make power out of, and the car that it is in is not really a "Halo" car such as the WRX or EVO's, this means that people will not have seen the value in spending time to reverse engineer the ECU so that it can be modified. Your choices are to leave the car as is, sell it and get a model that allows for mods to be done, or to replace the stock ECU with an aftermarket unit.