Sure, individual choices don't matter. My choice to wear a mask couldn't stop COVID either.

What matters are collective choices, made as a society. If everyone stopped eating meat, it would help.

But they won't. They'd rather die.

Of course it has helped. It may not have reduced the global meat consumption, because sadly there is still an increase through other people, but it has definitely reduced the current overall meat consumption in comparison to the scenario of this person having continued to eat meat.

Who knows how many of the people who have contributed to this consumption increase have considered reducing but decided that their actions don't matter anyway?