To answer your question simply: it's not just about the 'look'. For most of us, we practice flourishes for the dexterity and the feeling of self-accomplishment that the challenge brings (by having achieved something you worked hard for).
Granted, it may be seen as a 'waste' since very few make real earnings from it, but it is a fabulous way of gaining dexterity and feeling confident with your handling. Of course, if I were given the choice to perform either flourishes or magic, I would go with the latter without a second's thought. However, it is nice to be able to mess around with either when you feel like it -- and it is also a nice way to gain attention before a performance.
I'm not very good at flourishing but i still think it's fun to practise.. Whenever i can, i grab a deck and start practising.. So to me it's just a way to spend time, and i rarely perform flourishes for other people.. Just for myself and for fun.