I kinda have two responses here, so uh, here's both of them:
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Well, by the time this is an issue, odds are you've been a career politician anyway and don't need another job. This is just old people who refuse to retire because they like the power and trappings more than they care about doing their job.
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By the time they MUST retire, these ghouls have stolen sufficient money that it doesn't matter, and sticking around is just them refusing to give up the power and feed their greed even more.
Both seem equally reasonable and applicable to the problem.