As best I understand it, because in Perl 6, arrays always use the '@' sigil.

So elements of @x are accessed using @x[1]

And elements of the array pointed at by $x can be accessed using $x[1].

The abiguity that is confusing you is because Perl 5 used $x[1] to access elements of array @x.

@x = ( 1, 2, 3);;
print @x[1];;
Scalar value @x[1] better written as $x[1] at
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The explanation for that was that the use of the '$' signified that the element accessed was a scalar. But elements of arrays are always scalars, which makes the purpose of changing the sigil redundant. So in Perl 6 you don't.

In the same way, if it hasn't changed since I last looked, hash elements are addressed using %x{'foo'} (or %x<foo>) and not $x{'foo'} as now.