Because people are taking it as literally disappeared and haven't done anything. Helen Hunt and Kevin Bacon have definitely seen a drop in their workload but because Bacon had a supporting role in Beauty Shop, they act like he didn't "disappear".

Pfeiffer and Ryder both took hiatuses but they are back with films. Do they count?

The idea of top notch actors who are now slumming or working less than before is interesting but people are taking "disappeared" literally because it was never defined. The original examples were all over the place and the concept was never defined.