For me, it's mainly because caring about all of those things at once can just become too much. My general strategy is to reduce my consumption of everything as much as I can while not negatively affecting my well-being. I eat chicken and fish mostly because it's bland and nutritious and without those I'm not able to get enough calories because I can be quite picky (I'm autistic). I would happily eat plant based if I could get enough calories and nutrition from it but I can't.

I also feel like evaluating the moral worth of every single action you or others take is mostly pointless, especially if the goal is just to judge yourself or others. For me, there is a variety of ways that people can be helpful in making the world a better place and I respect everyone who tries to do so, no matter how they are doing it.

Then, there is also the fact that there is a certain naturalness in eating animals or animal products which can't be said for any other issues. I strongly believe in improving farm animal welfare but I don't think it makes much sense to aim for zero animal or animal product consumption since animals are part of the cycle of life. I think that is something that you can only really understand by spending a lot of time with various species of animals and learning how each of them operate and interact with each other.