Learning Options: Why would anyone ever short instead of long?

So I've spent my morning learning about options, futures, how they work, so on. One video I watched laid it out in pretty plain speak: A "long" is a contract that you purchase from someone else, and a "short" is a contract that you issue. Okay, simple enough. Graphically speaking however, "long" plays only have line go up, and "short" plays only have line go down, with the caveat being the flat line of initial investment +/- short/long respectively. This means that you can theoretically make infinite money on long plays, and lose infinitely on shorts.

So why would anyone even play with shorts? What's the incentive of writing these contracts to begin with if they can lose you so much money?