I have a challenge for you. Try live a month eating nothing except for seaweed as your protein source and test how easy and enjoyable it is to completely replace one protein source for an other which has completely different taste, smell, texture, and cultural place in your diet. Bonus points if you actually do not like the smell and taste of seaweed and have to work really hard with seasoning to eat it.
It is vegan. It simply just a very different diet from what you are used to.
Almost every culture has had a bean based dish, and eating meat with every meal is a relatively recent phenomenon in the last hundred years.
There's a reason why I replaced meat with beans and thats due to the flexibility and variety of dishes you can cook with it, across and within cultures.
And there we have it. It is about culture, taste, smell and texture.
All environment and cultures do not have beans in the center. The easiest examples are cultures which predominantly lived on fish.
In North America the three main agricultural crops are winter squash, maize (corn), and climbing beans. It should be no surprise that if you live there, cultural beans are great to you.
Like fish, seaweed is primarily part of the cultural diet in coastal locations. Look at the Māori people and there is a distinct lack of beans in their diet, but seaweed is used just as bean are in north America.
What you call "a hilarious false equivalency" is something I would call a lack of understand and empathy of different cultures.
Nevertheless, that’s the actual change facing most people if you asked them to switch to a vegan diet today. It’s not like they’re eating food characteristic of the 1900s today.
It is vegan. It simply just a very different diet from what you are used to.