I don't understand why you had to use 'map' to pass the regular expression

You could use map inside your sub, if you prefer.

Is it because when you run get_data( map { "^$_" @ids } ), it is like doing get_data( "^john" ) and that is being passed to the subroutine?

Not exactly. The map is like doing:

get_data( '^john' , '^james' );
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