Some foods are like that. For example, you cannot prepare Kosher foods with the same pots/pans/plates as non-Kosher food.
I guess you can invoke the mantra of “The Customer is Always Right”. The problem here is that the owners catered to a customer base that was fundamentally activist. I guess it worked for a while, but nothing lasts forever. I read once that very few restaurants last more than 3 years. And the reason is not just customers; you also have to survive the insane dictates of the local Department of Health. Had a neighbor who ran a popular Chinese restaurant and the local DOH drove him out of business. He could not get a 3rd mortgage on his house to meet their mandatory modifications they suddenly wanted for his restaurant.
That was patently obvious.
No sympathy whatsoever for the owner or the patrons both killing that state.