Let's imagine that shareholders agree on a 5 year return on capital plan. Now let's say some missteps/economic circumstances make revenue go down in the 4th year. The CEO will get heat from the investors. This is especially true if the board contains an investor representative who can vote the CEO out.

What choice does the CEO have at that time but to boost short term?

Look at the same story from an employee perspective. Imagine that employee worked for 4 years and the downturn arrives. They invested a lot of time of their precious life, much like the shareholders invested their precious money.

In the downturn, the CEO gets to make a choice and the choice ALWAYS is to boost the stock price for shareholders (and for themselves). Often, at the expense of employees.