I can attempt to answer your question GSB, although I can't say for certain, being that I don't work for a company that produces such foodstuffs or have any awareness of their market research on which it is presumably based.
I assume the answer is because they can. As part of the mindset to meat alternatives they wish to present the notion that the essence of food is it's flavor, not in it's content as an organism. In other words, by replicating the flavor of meat they are demonstrating how one has no need for animal products as a food source. Also vegetarians and vegans, like all people, have a desire for a variety of dishes, and don't just want to eat the same thing constantly.
It may also have to do with the fact that cuisine is a part of culture, so people identify with it accordingly as part of their habit of dining as part of their habit of everyday routine. This is also do in large part, I suspect, because many vegetarians were raised as meat eaters and that discourse of cuisine framed their dining habits.
Simply put, we can accurately call this dish a "cheese burger", because the concept of it is something that is identifiable to every American, even if it doesn't in fact consist of cheese or meat, but is soy or other alternative based. We could just as easily call it something else, and have it be the same thing, but not identifiable as the other. It's just a matter of convention.
Most veggies aren't generally all that opposed to the idea of eating meat, that is from a purely culinary perspective. It's the fact that meat comes from killing animals that they are opposed, from a moral standpoint.
It's a bit more complex philosophically for vegans, but I think that explanation will suffice to the point.
