A while ago, a company made the news for announcing that the minimum salary for all their employees would be $70,000.
Two workers ended up quitting because they were upset that new people got salaries similar to theirs, while they got small to no raises.
This is common psychological behavior-- once you achieve your social standing, you retain it by making sure you stay ahead of those under you. "Last place" aversion in games. Or colloquially, "Keeping up with the Jones's".
This is also a common argument against raising the minimum wage to $15 (or whatever number): "Well what about the people like me who are already making $15?" Great, you make $15, which is already a livable wage. Other people bringing $15 will not somehow lower your quality of life.
“The only time you look in your neighbor's bowl is to make sure that they have enough. You don't look in your neighbor's bowl to see if you have as much as them.” - Louis CK