The reason behind this is that when someone is switching to a vegan diet it's kinda hard to figure out what to eat. With vegan alternatives of food that he or she has eaten all life, it's a lot easier. For example, I like to add milk to my coffee, but as a vegan, I don't want to drink cow's milk, so I pick a plant-based alternative. I don't see a problem for non-vegans since it's often kinda obvious that the product is plant-based, it is almost always written on the package or something. And why fuss over the origin of words? Language works for its users and lotta words lose or slightly change their original meaning because of circumstances and I think it's normal.