Because it is an artifically maintained state.
If you have an awesome physique, you are one illness away from totally losing it. Or for a variety of other physical reasons, it could be gone within mere months.
And if you have a crap physique. You are just 6 months away from having a great body. If your diet, rest, training and supplementation is on key.
So when I see guys getting slammed for having a crap body, or guys thinking they are the shit for having a great body, it's all just dust in the wind. Either guy could pull a total 180 at any time.
For example. I was a 100 pound weaking before I started lifting. Then I became 170 pounds are hard muscle and looked pretty damn jacked. Then I stopped lifting and got into long distance bike riding and extreme outdorr sports and my life got busy, and I went back down to 130. Now after bulking up again, i'm almost back where I was at before and I'll surpass it.
You are not your car, you are not your job, you are not your physique, and you are not your fucking khakis.