I think there's some of that, but... no, part of it is because straight logic problems are... hard. And lots of candidates, even solid candidates who have held jobs in software engineering, can't write code with simple-yet-non-trivial logic requirements reliably.

"Write a linked list" won't tell you someone is a genius. But it will weed out a lot of people who can do "development" but can't hack.

And if you have a job that needs hackers (not all do!), these questions make for cheap filters that save everyone time.