To avoid giving raises and promotions, they put existing, well-trained on-call and hire new, untrained employees. When they puts you on-call, they give you little to no notice (usually a day or two), meaning that you have no time to find work. As such, most employees (even the best workers) are constantly worried that they'll be unemployed by next week. Workers are often pressured to work overtime for long stretches of time. There is almost no opportunity for advancement. The team leaders are wonderful and good at their jobs, but the company structure is toxic and exploitative.
Shameless favoritism, low salary, employee turnover and 0 level staff retention