They do it that way so people will click on it. Lots of X-Files fans will look to see if they recognize him but probably won’t, unless they’re also Fringe fans who recognize him from that. But if they referred to him as a Fringe actor, all those people who watched the X-Files but not Fringe wouldn’t even bother looking in the first place.

Seems pretty disrespectful to rank the importance of someone’s work by the overall popularity of a show/movie they appeared in rather than their relevance within it, just for the clicks/potential ad revenue, but here we are.