alter table impact on view

to my understanding, if I do alter table rename column, Postgres change the name of the said column, and modify the views using that table so that they keep working (NOT oracle behaviour..)

fine.

But if I alter table to change a column that is a varchar 20 into a varchar 21

postgres refuse saying that it cannot due to the return rule... using said column

why ?? as the view is not a materialized object, the impact of the length of a column of an underlying table do change the description of the view, clearly, but I dont see where the difficulty is "hidden". Can someone enlighten me?

thanks,