I personally believe that's why I occasionally desire it, as opposed to constantly.
Having stared at csv files with empty fields, I know what you mean, except that in that case the task can even be facilitated by the formatting of some fields. However there's a difference between say, fifteen adjacent commas and two or three. Anyway that's not something to be changed, so it's not worth discussing either. OTOH I often feel the need for some syntactical sugar to indicate a "missing something," whereas undef, however short, is somewhat obtrusive: Perl is already a hell to parse, but how 'bout a lonely minus sign?
my $x = foo(42,-,-,'cool');
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