It's the recursive trip through the filesystem that causes the problem.
Suddenly the stack space consumption becomes (N * greediest_filesystem) and
that has to be factored into all worst case calculations. It's a huge hole
to blow out of this severely restricted resource, so reducing N to 1 is a big
deal.
Also, as a practical matter, it's much easier to lay down a rule for
filesystem developers that reads: "thou shalt in no case use more than N
bytes of stack on your longest path" than "in no case use more than N bytes
of stack except on any symlink resolution path, in which case see the limit
on recursive symlinks to know how to analyze that path".
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