If I meet them at vegan events, I politely remind them that’s not vegan and go talk to someone else.

This might seem reasonable to you, but it's pretty fucking weird. Those people are at vegan events because they're interested in vegan lifestyle, plant-based diet, environmentalism, animal welfare, etc. I'm not 100% vegan, but I sure as hell enjoy attending events for people who care about making the world a better place like I do. Maybe you should accept that people have differences in their implementation of this philosophy and that they consider things like pragmatism, cost-benefit analysis, and flexibility to be more important than absolutism.