Too crap to keep, too expensive to sack
There's a certain "type" of individual - most often seen in ex-nationalised industries. They've been there since the year dot. Often it was their first, and only job. They started out as an apprentoid: 2 'O' levels and a budgerigar, and in the following decades rose up through the ranks to their current position: team member.
However, in their forty years of wearing a hole in the same chair, they have amassed one single, solitary, asset: their severance package. Based on years of employment and seniority for time served, even at the statutory minimum, they are hellishly expensive to get rid of. Given how much it would cost to axe one of these old-timers, you could reduce your headcount by four or five fresh-faced newbies.
And so they stay on. Not because they are actually any use, have any skills, or do any work. But because they are cheaper to continue paying than to fire - and salaries come from a different budget, too. They only occupy one desk (and can often be persuaded to "work" from home, so even that desk can be hot-desked to someone useful), keep their mouths shut during meetings and sometimes take the occasional phone message when you're unavailable.
So when companies make the calculation of how to achieve the maximum headcount reduction (i.e. ruin the greatest number of peoples' lives) for the minimum amount of money, these guys are untouchable. The moral of the story: being old isn't always the path to redundancy. If you can somehow survive and stay off HR's radar, you may, just, be able to live our your twilight years doing next to nothing, being paid for it and keeping your job security.