Because its a "novelty". One of my friends eats them as an addition to salads or sandwiches, she likes the aroma, so uses them as any other aromatic plant. Personally I like he smell of tomato leaves too, but I'm no so adventurous
I guess in a small amounts it will do nothing to you, if you are not allergic or with some liver problems.
Ok I have checked this and she is using them for the tomatina content.
http://www.ncbi.nlm.nih.gov/pubmed/19514731 So, kind of herbal use. You would have to eat 0,5kg to have the harmfull toxic level so I guess it's pretty safe.