I did 11 legendary raids yesterday in a town with 56 total gyms. We basically would disperse the group, each go to different areas of the town and watch until we saw something then we would post to raid chat when we found something. Of those raids we only saw 7 gyms. That's about 12.5% of the gyms that had legendary raids.
That said there were tons of other raids but people ignored them because they wanted Zapdos or Lugia.
I think this is a case of perception vs reality where just because the raids we see where not what we wanted there was a chicken little moment.