Tough sell for many affiliates. First off in the Midwest, Evening News is already sandwiched in the 30 minutes between local newscasts (I know it's a different story on the coasts). Second, the network would have to take that time away from affiliates who almost guaranteed have something that likely either gets higher ratings (i.e. WCCO and WDJT showing Wheel Of Fortune), or they have a local newscast in that slot where the station gets to keep all the ad revenue for themselves (i.e. KELO, KBJR, KXMB) and not have to share with the network.
Same argument for "forcing" the other networks to follow along with something that this panel likes, but still can't perform in the ratings. You first need to be able to offer them something that consistently proves to be better than what they currently have. If it were an optional add-on, perhaps you get a few affiliates to dump Inside Edition or ET. But if I had Wheel, and you wanted me to replace that with an add-on to a distant 3rd place newscast, I would tell you to pound sand.