I too am experiencing this magical phenomenon. I can stand to eat meat, but I can't particularly stand to prepare it anymore -- and I'm way too poor to order it at a restaurant. So I am a de facto vegetarian.
What's with the preparation if I may ask? I have a strong dislike for the meat industry, however I'm not particularly interested on giving up my meat. Perhaps if I lived in India or Thailand I would go full vegetarian because the food is awesome and diverse. The food ingredients where I live are rather dull even with meat on the menu so going vegetarian doesn't sound particularly thrilling. Anyway, as a solution of sorts I quite recently did my hunter's examination and am looking forward to reduce industrial meat from the menu.
Simple disgust. Prepping your own chicken, for example, really hits home exactly what you're doing, which is tearing apart tendons and such to get at fat and protein on something that used to be an animal. It's a personal thing, but I've heard others say similar.
I must be a freak. The more I cook, the more obscure the animal meats that I like. (Except horse -- I bought some in a supermarket in France and had only a crappy burner and a worn-out skillet. It tasted fine, but not worth the work I put into it.) (Kangaroo? Loved it.) In the other side of the coin, I only eat red meat down once a week. I often wind up vegetarian, but most days I will have one white meat dish (usually chicken). I've found that adding spice and making the greenery the most interesting part will make up for cravings. I've been more weirdest out by vegetarians that won't eat their veggies. Do you realize how easy it is to slice a big zucchini lengthwise with a mandolin, spray lightly with olive oil, broil on each side for 45 seconds, and then use as layers in a lasagna? Tomatoes, ricotta, noodles, zucc... heck, replace the noodles with eggplant slices (mandolin slice, leach with coarse salt for 15 minutes, rinse a couple times) and you don't even need much guilt. A lot of people associate "no meat" with "no flavor". Many vegetarians reinforce this with uncreative, Protestant recipes. Spice it up and you'll rarely miss meat.
Never heard of the word zucchini (I've always called it a courgette), but they can be so damn delicious as a main dish too, when you saute them. Slice them up, in a really hot pan with some oil. Throw some salt, pepper and a bit of lemon juice on them. They're the best if the edges are brown. Works great with broccoli too. I'm a lazy vegetarian. I often eat potatoes and some veggies for myself, and to put a third pan on my tiny cooker is more work (defrosting especially), so I just don't eat meat that day.
On the topic of climate change we could also consider the locality of the food ingredients (although I guess there are plenty of arguments in favour of either local or global). When I wrote dull, I didn't necessary mean bland, but rather the poor diversity in ingredients in my local ecosystem.