It didn't seem that obvious a term as you described it here, but a bit of googling gave the background:
It's effectively that the more desirable elements leave, the less desirable parts stay behind and get more concentrated... So the bad employees are the salt in the dead sea
It's effectively that the more desirable elements leave, the less desirable parts stay behind and get more concentrated... So the bad employees are the salt in the dead sea
It was coined by this chap https://en.wikipedia.org/wiki/Bruce_Webster#Career