To sum it up, because I love animals, I love the planet and I love myself.
I guess my "journey" began when I went vegetarian a year ago. I always wanted to become a vegetarian, but I thought I couldn't, because my parents were such terrible cooks that I thought I'd never start to enjoy vegetables or anything other than meat. I had already decreased my meat consumption ever since I found out that I had an alleviated risk for colon cancer and that eating meat would make my risk even higher. I even learned to cook a little and after a while I ate vegetarian five or six days a week. I didn't go full vegetarian though until I drove past lots of trucks full of animals (I assume on their way to the slaughterhouse) in a short period of time and I just couldn't help but think "Poor piggies, I'm sorry I'm doing this to you". Around that point my cooking got so good (I never cooked meat anymore, because the times I did I couldn't stop thinking "OMG this is a dead animal OMG this is a dead animal OMG this is a dead animal") that everything that had meat in it tasted terrible in comparison. So I practically had no reason to keep on eating meat anymore.
Now it was only after that when I started learning about all the other terrible aspects of animal agriculture. Other health effects, environmental stuff, shit that goes on in the dairy and egg industry. I mostly attribute it to the fact that whenever I looked for recipes, I automatically looked for vegan recipes, because I don't like dairy and cheese and I can't crack open an egg without thinking "DON'T get chicken period on your fingers DON'T get chicken period on your fingers DON'T get chicken period on your fingers" (yes, I made that connection years before I went vegan). Through that I came across all the information on the vegan lifestyle and honestly I had never even heard of 99% of the benefits. When it came to the animals, I had the same motivation as with the animals in the slaughterhouse truck: "I don't wanna do this to you and tbh I don't even like your secretions so why the fuck am I contributing to this shit?".
As for the environment, I'm always like: if you're a part of the problem, you're not allowed to complain. Now although we usually drop dead from colon cancer, we only tend to do that when we're really old. I'm 24 now and if I look at the average life expectancy in my family, I can expect to live for about another 70 years. Now I don't want the earth to be destroyed by the time I'm 94, because it would totally suck to live in a world in shambles at that age, but it most probably will be like that. But if I hadn't done anything in my power to reduce environmental damage, I couldn't possibly allow myself to complain about it. And I'll probably feel the need to complain about that situation in 2086. So in order to allow myself to complain about the environment on my death bed, I have to be as good to the environment as possible. And that includes going vegan.
As for my health, I didn't know going vegan had so many positive outcomes for my health. And vegans tend to look younger than they actually are, so that's a great motivation. I've also noticed that since going vegan, I actually got the motivation to work out for the first time in thirteen years, because now I can run without getting this bloody taste in my mind. So that's good too.