Honestly, I don't think the game is 'unfinished.' Would you call mobile apps 'unfinished' despite getting updates? Is Breath of The Wild unfinished if you don't have the DLC? No, of course not.
Games development is tough. A someone studying it, I can assure you, developing a game is not as simple as you'd like to think it is. First, you need to get your ideas, then you need to see how you'd implement them, then you implement them, then test, etc. ACNH seems to have been developed using an agile process. Meaning, they go through stages and keep updating the game. The first trailer seemed to miss out on some things that we see now. They most likely have the stuff for the first few holidays done.
However, having updates makes sense. Every game picks up when it gets updated/events/DLC. Nintendo is a company with professionals who look into the data and tell them the best way to get money for this game. Keeping a constant hype of events will most likely increase their sale. They're giving us an amazing game so I'm not gonna complain that they want to do things to earn more money. I still get that stuff.
Events being updated? I prefer that. The game would get boring when I knew I could TT to the events. Having to wait? Damn Nintendo I love that!! Keeps me focused on the game! (And I know many would share this sentiment).
Is the game unfinished? I don't think so. Things might be missing but if people really have an issue with that, do you really thing they wouldn't add that stuff in updates?
"We don't have this furniture piece!" Some items have only appeared in NL but that doesn't mean they're required to appear in NH.
I'm not saying it's wrong to think the game is unfinished, but there shouldn't be a whole 'this game is def unfinished' because hey... some people ARE happy about the game as it is. We're all allowed to have opinions but at least please understand that developing games is not as easy as many may think. Give nintendo SOME benefit of the doubt