Unfortunately, vegetarian is not the same as vegan (VGML). Vegetarian includes dairy and eggs. Hidden as well as overt. About 50% of the pasta sold by food service companies to the food catering companies have egg as an ingredient.
You do NOT want to know what happens when those two categories and myself get together! It's not just a matter of "Mom, the eggs are touching my potatoes again!". When that happens, I go into anaphylactic shock, which I really don't like to happen. I carry an epi pen on me at all times. If a VGML meal is prepared properly, I don't have that worry.
Aside from the ingredients (which is why I always bring my own food) is the question of why a D1 customer needs to bring their own food in the first place (aside from medical reasons like I have)? Why does a regular meal pax get a tub of Ben & Jerry's Cherry Garcia and VGML gets mushy cantelope? Don't the catering companies know that Ben & Jerry's now sells almond milk Cherry Garcia? Why can't that be used instead to make the pax feel more like a D1 customer? Why do they believe an grilled onion sandwich is perfectly fine to serve to a special meal passenger and not to a regular meal passenger? Why do ALL special meals feel like the unwanted step-child of the catering business?