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Shareholders want to see businesses grow their profit. Once you reach a certain point, it's easier to scale by doing lots of things rather than one thing better and better, and doing lots of things requires lots of people to do them. This creates a weak signal of "more employees -> more future profit". People buying shares (who effectively set the price) care about future growth, which makes looking at revenue enhancement directly a stale signal.

From the company perspective, this is still an alright state of affairs, because even when investors get skittish and less overtly speculative, the company can still improve profit numbers by cutting excess staff. Meanwhile in times of plenty, the hiring of that glut of employees drives the company value higher due to the speculation that they're going to be able to do all the things.

It's dumb, but investing is often a web of self-fulfilling prophecies. If investors think a company will increase in share price, they buy, driving up the share price, allowing the company to sell shares at a higher price, giving them more money to grow.