Nobody, and not the tag, is saying that primary sources shouldn't be used. But they are simply never enough to write a proper encyclopedia article. The tag should be appropriately placed on all articles that lack reliable and independent secondary sources to help draw attention to the problem (which it is).
If secondary sources cannot be come up with for a certain article, the question is whether that article should really have a place on Wikipedia rather than to absolve that page from the most basic requirements of an encyclopedia article. — aldebaer⁠