I received and email and saw the game discounted. Went to the store and it is nowhere to be seen. Searching online I was able to find the page on the store but clicking it is redirecting me to main store page. This is obviously region blocked for me.
Question is: why is GOG engaged in this region locking BS? Steam started this crap as well when every country got their own localized currency and whatnot. Yet here on GOG I am still paying in USD AND getting region locked? FFS.

Can I at least ask for the reason this game is blocked for me?

Not much of a sailor but the high sea is beckoning.

Ask your government. When something is region locked it's always because the government does not want game x being available for sale for whatever reason. GOG doesn't put region locks just for fun.

I'm not sure that entirely covers it. I'm in Japan and I can see TNO and TOB just fine on GoG, but TNC doesn't appear at all (even though I just got an email promotion about the current sale). I can also see all three titles on Steam here, so it doesn't make any sense from a censorship point of view.