Some bosses don’t love firing people and give people too much of a chance. We hired someone and I told the boss to fire him the first day, he was that bad. He didn’t, time dragged on and he never improved, he only got worse in new and spectacular ways. By the time it reached a breaking point it had been well over a year and they had to do a ton of paper work, track performance, give him a PIP… so many hoops. I think he ended up working for us for 3 years. We even caught him red handed lying to skip out on work, and his lie to HR to cover it up involved him using company equipment to run a side business during work hours (somehow they didn’t see that as a red flag). This was I the US, where when I was hired I was told flat out they could fire me with no notice and no reason. The company was always worried about lawsuits around firing people, so they liked to have all their ducks in a row.

It seems like it could be easy to make it through 6 months unless the company takes it really seriously.

In a large company, it's more likely for a manager to inherit an employee than to hire them. Often long after this six-month period.

At that point, the manager is just stuck with the net-negative employee.

After 6 months the employee is then free to do the bare minimum.