If I could have all of the benefits of working out without actually doing it, I absolutely would. However, that's not really how it works. While I'm in the middle of working out, all I really want to do is stop an sit own. But I don't, I keep going, and here's why.
I like to eat. If I would cut down on delicious foods I could probably have a killer body, but I really love to eat, and I don't like depriving myself. So much enjoyment comes from food! So by working out, I can allow myself to eat a bit more than I otherwise could.
Endorphins. Despite the fact that I may hate it when I'm doing it, exercise does result in increases happiness.
I like to be in shape. Someday I may have children, I want to be happy and healthy for them and have the energy and endurance to run around with them.