I think part of the reason for the shift to other routes is the availability of sites like this one, or the Facebook Camino groups, where there is a preponderance of voices saying "The
Camino Frances is overcrowded. Take a different route."
It used to be that the information a prospective pilgrim would get would lead them toward the
Camino Frances. Either they would have read a newspaper article, or a book, or seen a movie, all of which featured the
Camino Frances. Or they might know someone who had walked a Camino (most probably, the Frances). Then they might have done some research and found a "
Camino de Santiago" guidebook, which would also feature the
Camino Frances. Then they would go walk the
Camino Frances. Then they might like it and want to walk it again. Or they might be inspired to try a different route. But the
Camino Frances remained the foundation and received the bulk of the traffic.
Now, they hear about the Camino (maybe the Frances, but also maybe the Portugues or Ingles, or Norte or other route). And they come to a forum or group. And for sure there are some voices saying that the Frances is good for first-time pilgrims. But there are more voices, and more passionate voices, telling them to steer clear of that route.