I tend to the view that the uptake of veganism falls somewhere distant from the mean on the bell curve of types (from the most caring to the most uncaring). Put another way, about as many people as naturally lean that way are already veg*n and convincing people to truly be ethical vegans becomes less effective the further we travel towards the mean.
I think there a couple of ways in which the situation may be more optimistic than you think.
1 Societies seem to become more ethical over time. It's hard to imagine apartheid South Africa today. As recently as the 1990s, gay marriage was illegal everywhere. This could lead to more veganism over time as ethical standards generally improve.
2. There may only be a small minority of people that are caring enough to be vegan when everyone around them is a meat eater, but once you have other family and friends to encourage you, it requires less of a strong determined ethic. I'm sharing a graph from business theory that is typically related to the adoption of a product or technology but I think also an idea.
In technology, say smart phones, the 2.5% of innovators are the people who pre ordered the first iphone or queued up outside a store. The 16% of laggards are the ones that finally got a smart phone last year because everyone was nagging them about how it was just a hassle that they are the only one not in the whatsapp group. They didn't suddenly became more interested in smart phones.
The 2.5% of innovators - in veganism/vegetarianism, that's us on this forum. The 13.5% of early adopters sort of agree with the ethics (but less certain) and need to have a few innovators around them to copy and talk them into it. The 34% of early majority are the people that can see the ethical arguments, but aren't caring enough to do it unless it's very easy and they are surrounded by full vegan restaurants everywhere and vegan-label food has reached price parity and Beyond Burgers are all over the place etc. The 34% of late majority have no independent intellectual ethics at all really, their ethics are purely based on laws and societal norms, and their behaviour is based largely on copying others, but these people can become vegan simply because everyone is doing it and the evidence has become indisputable that veganism is healthy and ethically and environmentally better (this group won't ever look at science or watch documentaries, so they won't realize the truths about veganism until it just becomes common knowledge in all social groups, on the radio, on TV etc).
By now I'm talking about decades into the future.
The 16% of laggards are hopelessly resistance to change and have really no ethics at all in relation to food. They'll go mostly vegan because factory farming is becoming illegal, meat is becoming expensive as climate change degrades land and population increases and meat taxes are becoming applied, it is becoming a hassle to be the only one at a social gathering eating meat and everyone telling jokes about you and you feel the glares and disapproval, and is becoming annoying to be constantly worried about when you will be criticised in public, and because, after you gave up on the first two doctors and declared they were idiots, the third doctor still reccomended that greatly reducing your meat will give you a better and longer life.