I think the biggest issue, especially in parts of the US, is just cultural inertia. It's reallynot hard or.expensive to eat an easy, healthy and tasty vegan or vegetarian diet, but a lot of people, especially men, tie their identity up with eating meat.
I'm lacto-ovo veggie and the number of people who can't fathom that I don't eat meat (in the UK where it's really quite common) is mind boggling.
"What, not even fish?" 🙄 No, mate, if it has a face I won't eat it, but thanks.
People also tie flavours to specific foods. I have a friend who has a north African partner and they tell me often they'd go veggie if it weren't for their partners chicken "which is so much better than ours". No shit, he uses a fuck ton of spice and lemons. If you threw that on some veggies it would be a pretty close flavour experience. I get missing a texture (slow cooked beef? I miss that) but the flavour thing just doesn't add up to me.
It's not just that. At least where I'm from in the deep South there's a lot of associations of class that go along with being vegan or vegetarian. As in, it's generally associated with wealthy, higher class, out of touch people from afar and partaking in that is akin to embodying those traits.
There's also the issue of food being a very important medium for expressing love, friendship, and hospitality, and denying that (even if for valid dietary reasons) is taken as a slap on the face for many. When someone offers you their food, they're offering you their soul.
Don't get me wrong, I think that everyone should try to eat less meat and I care about the environment, but there's definitely gotta be an effort to strip the act and identity of being vegan of those classist associations (whether or not they're true) and get it to be normalized.