Perhaps by covering stories as a journalist, one moves farther left. It’s not like it _should_ be 50%, or that occupation and political orientation are independent
Additionally, America's "left" is very much the same as Europe or Canada's center/right. The argument could be made that there is probably a more even distribution if you don't use America's right-weighted scale.
Journalism shouldn't be a political thing, period. It should be about reporting facts, not opinions, and about being as objective as possible. If that gets you classified as "left or right wing" - then I think that's a different discussion.