Repurchasing apps over mac

I purchased civilization 6 on my ipad, and its a great game. I was thinking to try it on mac with m1 chip, but it turns out I need to buy it again. I don't get why this is happening with apple trying to make a universal experience for their app store across iphone, ipad and mac.

I understand they charge you seperatly when mac is still running on intel chips, since developers may need some extra effort to let the app run on different platform. But now if they could get an app run on m1 ipad, how hard is it to get it run on m1 mac?