For the same reason that this doesn't work:

my @x = qw(1 2 4 8 16);
foreach (@x) {
  print $x[$_], "\n";
}
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The value in $_ is not the index of the item being scanned. It is the item itself. So on the third iteration of the loop, you're trying to look at $x[4], and on the fourth iteration, $x[8]!

-- Randal L. Schwartz, Perl hacker
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