One scenario off the top of my head ...
Suppose the end of a term is coming up. A justice/judge is young enough to need to continue working after his term. A controversial ruling is coming up. The justice considers how the ruling will affect his job prospects - or - he is outright promised a prestigious position if he rules a particular way.
Then you have a corrupt justice and that same corrupt justice would take under-the-table payments and favors during a lifetime appointment too.
So you think a justice could be bribed with a job? Do you think they can be bribed under current situations? I am pretty sure really good lawyers can make way more than justices. And I’m pretty sure a former SCJ could make a lot of money in private practice. Should there be a mandatory retirement age or should we wait until they’re senile before removing them from the court?