Because the parens just create a flat list. What you wrote is the same as: 
my %hash = (
    'hi' => 'hello',
    'all' => 'bye',
    'later' => 'gone',
);
print $hash{'all'};

[download]
If you want nested hash references you need to use {}. Like this: 
my %hash = (
    'hi' => {'hello' => 'all'},
    'bye' => {'later' => 'gone'},
);

[download]
For more on nested data structures read references quick reference.

In reply to Re: Doubt on hash keys by tilly
in thread Doubt on hash keys by velusamy

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