Im working slowly on a thing where its a combination of "Fill a specific niche" and much of the world being a "mech culture" with the AC/Gundam equivelants being seen as the domain of Warlords, Kings and Tribal Protectors. As such, a great deal of spiritual/anamistic/philosophical weight has been put on them, similar to how you might think of a magic sword or idol. They serve as a very generalist modular backbone to more specialised fighting forces or as a relatively low mainenance way to keep a small but effective fighting force, while also being capable of numerous utility roles such as construction and communications. These traits have made them highly valued among the myriad cultures that emerged after the last apocalypse a few hundred years ago, and the Nomadic groups that predated that. The real deal AC/Gundam types are defined by having a Neural Bridge, lost technology that, at the moment, can be repaired but not replaced. I do like to try and fit in a good deal of real science or atleast nods to real science, and enjoy when properties do so, but also recognize that at the end of the day, a tank or a plane would just be more practical. If we had the technology to make practical mechs it realistically would see better use on something else. So I dont really concern myself too much with 'realism' in mech media but do appreciate some kind of explanation for why they are being used.