How deep is your regret for buying the GoG version of this and missing out on hundreds of workshop exclusive mods ?

For me, I would say about a 9. Shame there is no community or Mod platform here on GoG. Not even the Nexus can hold a candle to the abundance of Kenshi mods on steam. Feels bad lol.

I am aware of the downloader. But it's technically pirating and there is still no support for these mods as you can't post on the workshop. You can't even rate it or give feedback.

I'm just curious why so many mod authors choose to make their content exclusive to steam.

Well that's a new question that is totally separate from what you asked in the OP, and it makes little sense to ask it here, since as you say, those people don't use this platform.
Also no, it is NOT technically pirating, and you should banish such a silly thought from your head. All Kenshi mods are free.

Where else am I going to post it? Not on the nexus because the mods don't even exist there. And certainly not on the workshop as I can't even post there. Was actually trying to get a feel for what others think the reason might be. You're being needlessly obtuse about this whole thing. I don't see how the associated cost of intellectual property changes the fact that Steam finances the platform with which to host those mods, where the model itself prohibits Non-steam users from using the service. You're circumventing their right to exclusivity. Sounds a lot like piracy to me.

Why are you even here.