I'm sure they create a lot just for testing purposes, and only certain ones make it in.
Much like how we test many variations and ideas when building... and only certain ideas make into our final maps.
Just keep the best, and see where it goes from there, and you can always add more later. It's easier to add more blocks later than it is to try to take away problematic ones.
Canyon benefited from the environments that came before it. Hylis and team knew how the blocks would be used (generally) because of the rich history of track making in other similar environments.
But with ShootMania, it's a whole new ball game. Less blocks will be better at the start, just like there was very few at the start with the TMO Demo (although I hope there's a few more than that). ^_^