Isn't this similar to why people unfamiliar with that style of seafood would feel sick -- cultural views on what is and is not normal food -- and not because of their view of mortality?
Imagine that to cook that pork chop, the chef starts by butchering a live pig. Also imagine that he does that in view of everyone in the restaurant rather than in the "backyard" kitchen let alone a separate butchering facility hundreds of miles away.
That's the sushi chef butchering and serving a live fish he grabbed from the tank behind him.
When you can actually see where your food is coming from and what "food" truly even is, that gives you a better grasp on reality and life.
It's also the true meaning behind the often used joke that goes: "You don't want to see how sausages are made."
The issue most people would have with seeing the sausage being made isn't necessarily watching the slaughtering process but with seeing pieces of the animal used for food that they would not want to eat.
Some things just tickle the brain in a bad way. I've killed plenty of fish myself, but I still wouldn't want to eat one that's still moving in my mouth, not because of ickiness or whatever, but just because the concept is unappealing. I don't think this is anywhere near as binary as you make it seem, really.
Not to mention the millions of Americans working in the livestock and agriculture business who see up close every day how food comes to be.
A significant portion of the American population engages directly with their food and the death process. Citing one gimmicky example of Asian culture where squirmy seafood is part of the show doesn't say anything about the culture of entire nations. That is not how the majority of Japanese consume seafood. It's just as anomalous there. You only know about it because it's unusual enough to get reported.
You can pick your lobster out of the tank and eat it at American restaurants too. Oysters and clams on the half-shell are still alive when we eat them.
In case you missed it, you're talking to a Japanese.
Some restaurants go a step further by letting the customers literally fish for their dinner out of a pool. Granted those restaurants are a niche, that's their whole selling point to customers looking for something different.
Most sushi bars have a tank holding live fish and other seafood of the day, though. It's a pretty mundane thing.
The chefs butcher and serve the fish right in front of you, and because it was alive merely seconds ago the meat will still be twitching when you get it. If they also serve the rest of the fish as decoration, the fish might still be gasping for oxygen.
Japanese don't really think much of it, they're used to it and acknowledge the fleeting nature of life and that eating something means you are taking another life to sustain your own.
The same environment will likely leave most westerners squeamish or perhaps even gag simply because the west goes out of its way to hide where food comes from, even though that simply is the reality we all live in.
Personally, I enjoy meats respecting and appreciating the fact that the steak or sashimi or whatever in front of me was a live animal at one point just like me. Salads too, those vegetables were (are?) just as alive as I am.