For their style of filming, open courses are tougher to film. Specifically from the perspective of the catch cam. On a wooded fairway, the catch cam operator has to be fairly confident that all the shots are going to come on a particular line so he can set up in the best spot to catch those shots. In an open fairway, there's a whole variety of lines the players can take...hyzer, anhyzer, roller, forehand, backhand, etc. And the camera not only has to figure out which line the player is taking but also where to stand to best capture it. And if you have four different players throwing four different types of shots, the best place to stand won't be the same for all four.
The idea that open courses are better for filming I think is based in two antiquated notions. The first is from how ball golf tournaments are filmed and the expectation that disc golf should be filmed similarly. That is, "tower cameras" that don't really move around but rely on zoom and focus to cover a given hole. Can't really do that effectively if there are trees everywhere. The second is simply the technology of cameras. 15-20 years ago, all that was available was standard definition video tape. It made it harder to see and follow the discs in flight. So the less that could get in the way or obscure the view of the disc, the better.
Now with 1080p/4K cameras and what can be called a more guerrila filming style (cameras on the ground moving around for different angles and views), all those old concerns are out-of-date.
Wide open courses are still better from a gallery perspective simply because there's more room for a gallery to watch without potentially being in the way, but on the video side, there's no real benefit. At least until we get ESPN money to film and all those hard-wired cameras for the live TV broadcast need to be more stationary "tower" style.