I'm all over the place.

When I'm not dieting, I'm pescetarian with limited dairy, and I only eat fish once a week at most. But when I'm dieting, I increase fish to about 2x a week, and include dairy and even gelatin. I also eat eggs if I can buy them from local farmers, where I can actually see the chickens and their living conditions (only in the summer... I just can't make the drive in the wintertime). It gives me more options.

I was vegan for about two years, but it was really difficult to obtain protein sources: I could only eat beans/lentils 4x a week without getting sick of them, and it turns out I have can't digest soy -- which took tofu, edamame, tempeh, soy milk, etc out of the equation. I was also a high school/college student at the time, so I couldn't afford a lot of vegan protein stuff, which can be expensive.

I didn't lose or gain any weight during that time, but my bloodwork went really weird, so my doctor strongly recommended I eat fish or eggs. So I just cycle between them, depending on fresh availability. After undergrad, lactose-free milk became more widely available, and I slowly started incorporating dairy into my diet - a latte here and there brings up my fat and even protein macros easily.

So, yeah. When I'm dieting, I'm already limiting my options -- being vegan (where I can't have any soy) would just make it worse. You get more bang for your buck if you eat fish and dairy, and feel much more satisfied. It could just be psychological, but I feel like it's a very different fat/protein source than beans, even if you eat similar amounts of calories. Mentally, I just feel better when I include fish.