As the question has been answered adequately, I shall confer my own reason for transitioning to veganism that does not entail moral considerations and is distinct from the considerations evinced in other answers.
Expressed succinctly: my transition was experientially induced.
After perceiving the developmental and intellectual benefits of no fap, and understanding that this practice is suitably conducive to my principal ideals (developmental and intellectual actualisation, clarity and vigour), I pledged to myself that I will dedicate my efforts to the sustenance of this practice by renouncing onanism (and perhaps sex) altogether. This is distinguishably called celibacy.
About two years proceeding this revelation, bacon and egg sandwiches were becoming increasingly grotesque with each bite, and so were other animal products as a result (except beef). Eventually, there was this faint suspicion that 'I might go vegan' in the back of my head.
I quit bacon and eggs altogether due to how sickly it had become. I continued eating beef nonetheless. I started preparing my own burgers with ground beef -- and I enjoyed it. But veganism was still roaming around in the back of my head.
I decided to try a plant-based meal, a curry consisting of tofu and vegetables, the night after eating a home-made beef burger. It was markedly obvious that I did not experience the chronic lethargy that was the natural outcome after having eaten meat. I realised that I derived energy without feeling tired or struggling to digest my food.
The night after I had another beef burger. My last animal product.
What I realised immediately is that eating meat, compared to eating plants, drained my intellectual energy -- I could feel a slow descent from wakefulness to inertia. I find this sensation contemptable, and it is precisely this sensation that is antithetical to my ideals and the practice of celibacy because the descent of energy would counteract my intent to raise the energy (focus) into my mental faculties.
Note: this practice is not religiously motivated, but may entail spirituality.
This descent of energy, I observed, increased the likelihood of nocturnal ejaculation (wet dream), which compromises the practice of cultivating energy, whereas plant-based meals did not.
Essentially, it was this experience of chronic fatigue and intellectual inertia that repulsed me and repelled me from eating animal products again. I went vegan overnight and realised the intellectual and moral consistency of this practice later with further inquiry -- especially when I was brave enough to watch footage of the animal holocaust.
After assimilating the implications of eating meat compared to plants, it was imperative that I make the transformation -- especially if I am genuinely concerned about and value my developmental and intellectual welfare.
Which I do.
And so I did.
And I would have done it earlier if I ever had a plant-based meal to make the distinction that I needed to make.