Social media is itself as temporary as any social gathering, nightclub or party. It's the people that matter, not the venue. So when the trend leaders of one social niche or another decide the place everyone is socializing has lost its luster or, more important, its exclusivity, they move on to the next one, taking their followers with them.
I have little hesitation in saying that as a result a sickly pall now hangs over the big bang theory. As I have mentioned earlier, when a pattern of facts becomes set against a theory, experience shows that it rarely recovers.