Resources are limited and AFAIK either you build from the ground up to support modding, or later it’s difficult to implement. Also, and this especially goes for this
While the game is nowhere approaching a finished state this is a wasted effort.
Edit: doesn’t mean that there might not be modding support and custom options at some point. I’m pretty sure that custom (“second wave”) options will happen eventually, and I hope that so will modding support.