There's a few reasons for this. Firstly, the purpose of the mod is to be early game robotics, once you have roboports, you also have the technology to make robots, so you can just use regular robots. You just have to set up the production chain.
It's the same reason why the equipment cannot go into modular or power armor, once you reach that point in tech, it's no longer "early" game, and you can just use the more affordable base-game robots.
As for practicality, allowing them to work in roboports shouldn't be different from allowing them to work normally. I can look into adding it as a setting, so that people can choose for themselves whether they want it to work or not.