Also, in addition to the other useful statements here: don't underestimate how much of a corporate herd mentality it can be. (It's not one [hard data] or the other [herd mentality], it often seems to be a conflux of "both".)
It's not just "all my friends are doing it": the number of people that are board members of any company are a shallow pool. Board members often sit on multiple companies. Similarly large "professional" shareholders that take an active interest in corporate planning, have large voting blocks of corporate stock, and have an easy word with the board (if not a de facto seat on the board) are a relatively shallow pool (with some overlap).
Sometimes "all my friends are doing it" is the same people telling both the goose and the gander what's good for it. Even when it isn't necessarily the exact same individual person, it can be the same "families" (sometimes literally, there is a lot of inherited wealth in the board member class, but sometimes just metaphorically in cases like mutual/hedge fund management groups that use different hands-on managers for different companies in the same industry but still have shared short term goals for their funds).
Again, herd mentality is rarely the sole reason (and legally cannot be the sole stated reason because that would invite "easy" anti-trust investigations if regulators aren't asleep at the wheel), but underestimating it as a factor risks ignoring the way companies are built and the contributing factors of sometimes deeply and surprisingly shallow board and "activist" investor pools. (It also risks ignoring the warning signs of hard anti-trust investigations that could be worth doing, if regulators aren't asleep at the wheel.)