Why do I have to do a type cast in the ELSE part of a PostgreSQL update statement using a CASE, but not in the WHEN part? - postgresql

Question

I have to update a newly created metadata table (which holds a 1-1 relations with a person table) in PostgreSQL (>=12):
UPDATE public.metadata m
SET print_status =
CASE
WHEN p.print IS NOT NULL THEN 'done'
ELSE 'not done'
END
FROM public.people p
WHERE m.fk_people_id = p.id;
but I face this error:
ERROR: column "print_status" is of type print_statuses but expression is of type text
LINE 18: CASE
^
HINT: You will need to rewrite or cast the expression.
SQL state: 42804
Character: 477
print_statuses is an enum containing ('done', 'doing', 'not done'). And the print_status column of the metadata table is of type print_statuses (it also defaults to 'not done', so I wouldn't need the ELSE part anymore I guess).
It seems I do have to type cast the 'not done' text in the ELSE part of the CASE statement like this for this query to work:
UPDATE public.metadata m
SET print_status =
CASE
WHEN p.print IS NOT NULL THEN 'done'
ELSE 'not done'::print_statuses
END
FROM public.people p
WHERE m.fk_people_id = p.id;
Why do I have to do a type cast here, and not when using a simple UPDATE statement as in:
UPDATE public.metadata m SET print_status = 'not done' FROM public.people p WHERE g.fk_people_id = i.id;
?