People start to become vegetarians for various reasons. Some do it to become healthier. A lot of people know that meat, specially "red meat", increases the cholesterol, is full of hormones and antibiotics and other substances to make the meat "look good", that can be harmful to their health. This alone should be a very good reason for giving up the meat. However, most people seem not to want even to think about it, incredibly.
Some do it solely out of compassion for the animals. In my case, I started
doing it for the animals, more than two decades ago after attending to speaches and reading books about karma and spiritualism.
Latter on, I became engaged in Vaisnavism.
I became a truly vegetarian in 1999, finally banning eggs from my diet.