The CEO's job is to make the company valuable. That's kind of a sociopathic view, of course (gee, I thought our job was to make heart valve replacements or whatever). But, that is the trade off you make when you go public. And, just in case it isn't clear, stock price + dividends over time should equal the cash flow generated by the company. So, looking at stock price over a ten year period is a decent proxy for evaluating a CEO's performance.

Only decent, and only proxy. Say you worked the first 5 years propping up a dying business, and the next 5 years building a bunch of incredible value. The stock market may not have reacted to that, but your company is set to explode in value. Or you may have started in a bubble, or finished in a bubble, or...

So of course it is not the only measure, but it is certainly an extremely large part of measuring a CEO, since it is his job to maintain and/or grow the value of the company. It will never tell you if the company is bettering humanity, good to its employees, or other very worthwhile measures.