This is something I think only vegans can understand without it turning them off veganism. Pls don't think I'm arguing against veganism because it's quite the opposite. I'm identifying what I view as the biggest obstacle to mass adoption of vegan/plant-based diets: Availability of nutritious plant-based foods. However it's important for this topic to stress that nutritious plant-based diets are perfectly possible, all the science and evidence proves it. Also, in practice in almost all cases it seems like it's possible for people to obtain those foods (and supplements if needed, which they aren't always, not that there's any problem with supplements but that could also be a turn-off for some people who are opposed to supplements for some reason; it's possible to get adequate plant-based nutrition without supplements. It can however help and it would be good if people were open to taking supplements, especially since they can be useful for any diet).
I think there are just a few areas where availability of plant-based foods could be improved, including having more fortified foods available (which I think people should also be more open to eating, since they're safe and effective and can be important sources of nutrients). I think a lot more foods should be required to be fortified with B12 (and maybe other nutrients like vitamin D, iodine and DHA/EPA) by law, just like how a lot of products like grains are already required to be fortified with some nutrients by law but people just don't know they're already eating fortified foods, and since animal products are already mostly fortified anyway by way of supplements and fortified foods fed to animals, so replacing animal foods with plant based foods in a society would seem to indicate a need for an alternative food fortification strategy than the one already in place.
I also wish seitan was more available, since (aside from for gluten intolerant people, for which there are other foods, and people often have different allergies to things but there's almost always an alternative), it's one of the best, most tasty, healthy and nutritious plant based sources of high protein; and can work very well as a mock meat that people enjoy.
I just think if plant based foods were more accessible, and there was more widespread food fortification of nutrients of focus for vegans, to make it even easier for people to get enough nutrition on a vegan diet, it would be one way we could say "You don't even have to think about it, just eat the plant-based foods available." And know that they wouldn't even need to learn about what plant-based foods to eat for healthy nutrition, and would be fine either way.
I heard a quote in The Morning Show :
"People don't know what they want until we puree it, spoon it up and make airplane sounds."
that reminded me of people not knowing what's best for them, animals and the planet (vegan/plant-based diets), and how we need to make it as easy as possible for them to follow.
To me, fortifying as much food as we can and making it as simple and straightforward to get all nutrients on a plant-based diet as it possibly can be, would make people more open to and confident in eating them. Even though it's perfectly doable already.