i think they just don't care because there is new arma game coming soon so they are focused on that front. game is roughly 11 years old, so i doubt they would pour their effort to revive dead game, too many issues with bugs delayed fixes it means only one , they are trying to get all from dayz before it looses player base, at this point modders are doing more than Bohemia , 11 years have passed yet they didn't even add new transportation system(helicopter, train etc.).

If wonder if in developers will add mechanics for railways , because it's good transport for those who didn't find cars , you will need extra tools for fixing or gathering parts, if that mechanic will be added it would mean power plants will no longer be used as decoration for the map on top of that they can add light systems too for cities. i know it's overkill for trains but it would be universal transport because with it you can transport loot(containers, barrels, wooden boxes). it will force players to use pas and radio systems in order to avoid collision between trains or cars.