I would go vegan if there were more varied protein sources than those that come from fungi (which I am intolerant to) or beans and pulses (which, tmi, make my IBS flare up horribly, as does soy and tofu). I was very ill the first time I tried quorn as a teenager and since then I also physically can't stomach mushrooms.
I think secondary to the above is the amount of faff involved in checking ingredients, severe limitations when eating out, having to cook from scratch a lot more when I'm already busy. It just seems like a lot of hard work, which puts me off. If it was quick and easy to be vegan, with more variety of protein, it might convince me.
I get that for people that are deeply invested in animal welfare, the work involved in being vegan is worth it, but personally, I want farm animals to be treated better, but also believe that as many breeds wouldn't have existed if it wasn't for human intervention, I don't think it is inherently immoral to kill animals for food.
If I was going to be vegan, it would be for environmental reasons, and honestly I think a lot of the vocal vegans would do better at convincing people if they took this tack, rather than the, for example, "you must hate animals to eat them and are probably a terrible person" strategy that two of my family are currently doing on FB.