I don't think I'm artistic enough to judge flower arranging. So while I think they can be beautiful, I am not a big fan of purely subjective competitions. I will have to say that I am ok with things like skating, or gymnastics, and the like, where the level of difficulty of the move is considered. I find that difficult to determine in something like flower arranging.

For my suggestion on what to add to the Olympics, maybe rock stacking. They can judge the height, the rocks used [smoother rocks get bonus points], and they can even add aesthetics if they want. As for the why, it requires good concentration, skill, and decision making. It is something that everyone can do, but only a few can be masters of, which is perfect for Olympic sports.