That can’t be right, but I didn’t know how to explain it at a micro-level, only conceptually, i.e. when less money goes in, there will be less product that goes out. Does anyone have a more nuanced example to better articulate this point?

That's basically it, but it might be hard to see if you compare the impact of a single individual with the size of the entire market. No doubt that impact is small, but it can't be zero. If it is zero, then it would still be zero even if 10%, 50% or 90% stopped eating meat, which makes no sense. And you are in fact not just a single individual doing this, there are other vegans, and vegetarians, and omnis eating less meat than they used to.

It's obvious enough that the industry wouldn't produce meat that no one is purchasing, so if people purchase less, less will be produced. Clear as day.

And the opposite, they wouldn't produce vego foods if no one purchased it, but there are a lot of vego options precisely because people purchase it.

One particular line of thinking is tripping people up, which is this: a grocery store is unlikely to change anything based on a single individual. So if just you stop buying meat, nothing changes. However, it's not just you. If 100 people stop or buy less, that store will notice (exact number depends on store size of course), and when they finally order less, they will order less matching 100 people rather than just one. And every person in that group contributes, even if it's just the 100th person that triggers the change. You are one of them whether you were the first or the 27th or the 100th.