I think another possible reason for reality TV’s ratings trouble is that reality shows suffer from the same problem as serialized scripted shows: their impact is cumulative, and you have to watch many episodes in a row to really get into them. Reality isn’t the same exact thing as 24 or Heroes, but it has a certain kinship with them — remember, part of the idea of Lost was to make a scripted show that used some of the things that made reality shows involving, like watching to see who would form alliances and who would have to leave the show. (Lost is like Survivor except that, as a non-reality show, it can kill the characters off instead of just voting them off.) Part of the reason reality shows were so much more involving and exciting than most scripted shows in the early ’00s was that relationships and storylines really built week-by-week in an organic way.
But it’s hard to watch just one episode of a reality show and get much out of it, even reality/game-show hybrids like Deal Or No Deal. So like their scripted cousins, people turn away from them and toward shows where you can get a complete half-hour or hour of entertainment — hence the improved ratings performance of sitcoms, the ultimate “drop in any time” TV.