Why gform_field_value works for a text field but not for a dropdown?

add_filter( "gform_field_value_text_field", "populate_text_field" );
function populate_text_field( $value )
{
   return "Dynamic populated";
}

add_filter( "gform_field_value_dropdown_field", "populate_dropdown_field" );
function populate_dropdown_field( $value )
{
	$value = array(
		array( 'text'=>'Foo 1', 'value'=>'foo1', 'isSelected'=>false, 'price'=>'' ),
		array( 'text'=>'Foo 2', 'value'=>'foo2', 'isSelected'=>false, 'price'=>'' ),
		array( 'text'=>'Foo 3', 'value'=>'foo3', 'isSelected'=>true , 'price'=>'' )
	);
   return $value;
}