Why mine over buying coin?

I'm new to this, and based on some numbers I put in on whattomine.com, it looks like the payback period is extremely high -- nearly a year for mining ETH today, assuming no difficulty increase? After a little research, it looks like the difficulty increased 3x in the past 4.5 months, which means that the hardware becomes obsolete.

Has anyone done a side by side comparison of mining vs buying the coin? Why would you choose to mine?