They won't switch networks because ABC is owned by Disney which owns Marvel so they use Agents as a way of promoting the MCU movies. It's why even though the show doesn't directly tie in with the MCU there is always a ton of commercials for the movies shown during the show.maybe market flooded wi too much superhero stuff.
CW has two or three going I think. and they're happy with lower ratings.
wonder if it would pay for them to switch networks
I think they just lost their way a bit once they got past they initial inhumans & Hydra stories. The current season is meandering around so much that even fans from the beginning are losing interest. If there is a S6 I really hope they reboot the show a bit and take it back to it's beginnings of SHIELD being the good guys and not in hiding.