In short: Too much scenery, too little mountain bike. You need to get wayyy closer, either with longer glass or physically closer. You've caught a good moment in each scene, but I really want to be close enough to see the rider's face. Looking at the first image, I'm thinking shooting from the fork of that tree image right with a moderate telephoto, or right from the edge of the mound with a UWA would have made for good shots.