Look up Talkwalker, Hootsuite, Nexalogy, etc. Governments and other institutions use these tools.
Spreading the conversation elsewhere doesn't change the ability of these analytics platforms to cover them, although it does introduce more noise into the signal; the smaller the forum, the less an impact it has in the analytics rankings. If you slice up the pie into a ton of tiny chunks, the data received becomes less useful.
That said, some of the uses of these platforms are completely reasonable and very pro-social. We kinda want law enforcement to know if Jimmy Bullets just posted that he's gonna shoot up grade 4 English tomorrow.
I suspect that these tools are all looking at the world's largest social networks with 9-10 figure user bases. The same argument applies to them: they're too big. None of them should exist. Once you break it down to thousands or millions of different platforms, each with much smaller user bases, it becomes prohibitively expensive to surveil them all.
> We kinda want law enforcement to know if Jimmy Bullets just posted that he's gonna shoot up grade 4 English tomorrow.
Has this ever prevented a shooting? They always find these posts after the fact.