Sounds to me like maybe they aren't as knowledgeable about vegan food. Or, perhaps they just don't have a lot of vegans coming in so they are lacking experience. I've learned to not only ask about meat/lard in the ingredients or cooking process but also about chicken bullion, gelatin, sugar, enzymes, natural flavors, etc, esp in tortillas. If they don't know I request their ingredient list and most of the time, the servers are very understanding and end up appreciating that they learned something new, and some have even said they'll share it with the team for future vegan customers.