because $1, $2, $3 ... are dynamically scoped to the current BLOCK.
see perlvar

$_ = "aaaabbbbcccc";
if ( not /^(\w\w)(\w\w)(\w\w)$/ ) {
    # inside a block
    if ( not /^(\w\w)\w\w(\w\w)\w\w(\w\w)\w\w$/ ) {
        die "failed";
    }
    print "inside: $_ = $1 $2 $3\n";
}
#outside a block
print "outside: $_ = $1 $2 $3\n";
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