It comes at a small cost per news item, just like email spam costs, which added up would make it very annoying to work as a journalist.
In order to avoid getting spammed, they would have to do exactly what we would like them to do, which is to fack check.
Besides, contrary to what happens with spam, it is not cost-effective for a single individual to do this on a regular basis.
However, I wonder if it might be cost efficient for a community to do this, and whether it is done in any other community to keep the quality up.