Maybe instead of a complaint make a simple very specific and clear request, like can you please make a chicken breast and cucumber salad with vinegar for me, maybe a bowl of broccoli and onion dip. Maybe other people will ask after you do it. Sometimes people just don't know what to do and with all the food issues people have it can be impossible to include everyone seems best to just be very direct. My kid had a peanut allergy friend and the mom told me to read the labels, ummm a level of responsibility I am not prepared for so I pressed for a list and when I got one it was easy.
You can also teach by example and bring a few things with a note saying the thing diabetic friendly so people know, it can be tricky for people.