Familiarity of taste and texture makes the transition easier for some folks. For most people, though, the transition isn't terribly difficult. What happens is that people slowly shift toward a more plant-based diet and suddenly realize that they're there. They find that they never go back to eating meat. You decide how and why you do it.
People often decide to eat differently for health reasons.
A diet low in fat, cholesterol and rich in fiber is strongly associated with lower risks of heart disease, cancer, obesity, diabetes and hypertension. They run less risk of ingesting of toxins, pathogens and contaminants than meat-eaters. Pasta and bagels and french fries won't cut it. Fruits and vegetables alone won't, either. You should eat a wide variety of fruits, vegetables, whole grains, seeds, nuts, legumes and soy products.