Honestly, I really wish I could. Health benefits, ethical arguments, all the "logic" is there in my head. But I just can't do it. For me, the meat-alternatives are just not good *and* convenient enough yet. (and just to be clear, I am in absolute awe of people who can make it work. I'm very impressed by the strength and intelligence required to make and commit to that change given the culture I live in)
I live in San Francisco, a city with more vegetarian and vegan food options than most other US cities. If it's hard for me to find easy/regular/cheap access to vegan options, I can't imagine what it is like for people outside of a major city with sizable vegan/vegetarian populations. Places like Burger King picking up the Impossible burger makes me REALLY optimistic on this front and I try choose this option as often as possible.
Also at play: most vegan food just doesn't taste good yet. Again, I live in SF. There are lots of options here, but most times I've had a meal at a vegan restaurant or a vegan item, I almost always regret it from a taste perspective. This is a little glib, but when vegan friends tell me that "vegan food is delicious!" I usually hear "I have been vegan so long that I have forgotten what bacon tastes like." I fully admit that this is a profoundly shallow excuse. But for folks like me that haven't made that life change yet, it's a huge bridge to cross in terms of supporting a long, lasting dietary change. I wish that more vegetarian/vegan folks would not minimize or handwave the significance of taste differences between these diets. Maybe in their experience, it's not a big deal, but it isn't everyone's experience. And maybe right now that taste difference is real, but things like the Impossible burger really help me see a future when I can make that switch for good.