Part of the problem may be that your mom does not know what the food truck is like. where I live - the only food trucks you see are at construction sites and very likely are someone running an illegal business (not drugs, I mean they don't have proper licenses and all).
I am aware that there are "gourmet" food trucks in other cities, I've just never seen one. Have you tried showing your mom exactly what you mean?
I'll try that, though she had a hard enough time with the fact that I wasn't getting married closer to where she lived (in an expensive suburb where everything is about 3x our budget).
I think that the bolded supports goldilocks's theory (which was what I was trying to say, but she was much more articulate!). I have often seen something like this happen: someone else's mental picture is very different from what you are envisioning.
My husband wrote a klezmer piece for our wedding music, and although she didn't say a word before, my mother told me afterward she was picturing a few bedraggled, scruffy amateurs in old-world costumes screeching on fiddles; she was very surprised when they turned out to be professionals from the symphony orchestra in tuxedos (and she loved the music). Like that.
If your mom lives in an upscale suburb, she may never have seen nice food trucks. I live in a city with a lot of good food trucks. The ones nearest my suburban area are little taquerias; the food is yummy, but the trucks are run down and surrounded by blowing napkins and such, and the food is great for a quick lunch but as much as I love it probably wouldn't work well for a wedding reception; it's made in very small batches and isn't very fast. There are terrific ones elsewhere in town that would (and I know already have) work great for parties, including wedding receptions, but they are rarely seen outside of young, hip neighborhoods and business areas at lunch time or at festivals. Is that true in your city, too?
probably have fabulous food, but I agree they seem less wedding-y (even for a casual wedding) than these
So your mom may very well be picturing something entirely different from what you are envisioning. Consider that before chalking it up to her being a "snob" -- anyway, she may just have different tastes, and labeling and name-calling never get anyone anywhere good. She doesn't have to be wrong for you to be right.
Her objection may be entirely different from that, anyway. I know my father would have disliked a food truck wedding -- not because of any question of taste, just because he hated waiting in line. He would've disliked the fanciest, most upscale buffet, too, for exactly the same reason.
By the way, in looking for these images, I saw several with wedding couples, so you might be able to google around and see if anyone who's already done it has any advice based on their experience. I noticed food trucks were popular at graduation parties here last year.
Whether the food is casual or fancy matters less, in my opinion, than in whether the truck(s) you choose have experience with serving large groups -- not just in cooking large batches, but getting it served hot and fresh to large groups. I adore my favorite taco truck, but it probably would be a disaster for a wedding reception or any large group. In other words, the same as any other food provider, they have to know how to cater a big party, not just cook delicious food.