As I've said a few times on this thread, I never don't take my own foods to BBQs (and I go to quite a lot of them) unless It's close friends/family who insist I don't need to and whom I know will get things I'll like/aren't going to be causing themselves stress or spending money they don't have. It's good to ask what people would like to eat, generally! If I was having people around for dinner I'd likely ask if there's anything they particularly DON'T like, or if there are any requirements.
Yes my diet is very normal for me, but vegans are still a minority, I'll likely be the only one there and the BBQ hosts might not know what to get-taking my own avoids them mistakenly buying vegetarian burgers instead of vegan, for example. If I was someone who didn't like faux meat, again-taking one's own prevents the host buying something that won't get eaten-veganism isn't something many people are interested/experienced in still.
I went to a large, organised BBQ at my partner's sports club recently. They had potato wedges for everyone, fine for me too, and we took two vegan burgers for me, cooked wrapped in foil. Ketchup's vegan as is chilli sauce which I added to the burger. Bit of rocket in the buns, that's me fed, no drama, and not requiring a lot of thought processes or creating of a lot of 'special' dishes.
This is only me personally, but I'd not be happy if a host, for example, told me they had it covered, insisted I didn't bring my own things and then only provided a green salad-salad has been mentioned a lot on this thread! It's a nice addition to burgers/other BBQ sandwiches, but BBQs often involve booze, and even if they don't, I'd be starving and sloshed if I'd only had a salad sandwich.
My Mum has done this before! Albeit a long time ago. I got used to taking my own and repeating the phrase 'I am a vegan, not a rabbit' quite often. But again, vegans aren't a homogonous group and some prefer to not eat faux meat etc.
It isn't the best for us, I agree. It's very processed and salty. But It's not going to harm anyone if only now and again.