Because they're yummy, or at least some are :) Breaded vegetable masala burgers, while not exactly health food, are delicious! As are spiced homemade black bean burgers.
Some brands also offer easy protein for few calories (Boca vegan burger= 70 cal, 13g protein), so they're helpful when on a diet.
I don't get meat cravings at all- whenever I get a whiff of uncooked meat, I gag. Even if I did, I don't think veggie burgers taste a lot like meat.
We aren't against the taste of meat- most of us are against how the animals are treated, or the impact it has on the environment. Since veggie burgers are tasty, convenient, and sometimes nutritious, without all the cons of meat, why not?
And on the contrary, I know very few vegetarians who claim we were not meant to eat meat. Anyone sane is going to recognize that we are naturally omnivorous. Its natural, but that doesn't mean its necessary.
And, thanks for asking your question in such a polite way :)