Why only one statement and reason per line on proofs?
At Vohra, we don't just encourage accuracy; we also ensure efficiency. If you are consistently accurate, but take ten times longer on each problem than everyone else, then you have no competitive advantage.
To do this, we make it harder and harder for you to be inefficient. At first, a little inefficiency is okay. You're learning. But, you will always have to repeat every problem until your solution uses the most direct methods, and can be completed in a timely manner.
In Geometry proofs, this is especially important. We don't want you blindly proving that every single pair of vertical angles is vertical, or finding and identifying every set of corresponding angles in a set of parallel lines. That doesn't indicate learning, and it will take forever. So, we give you this incentive to be more efficient, and to only prove what is necessary: You must put only one statement and one reason on every line.
If you want to prove every single pair of vertical angles, supplementary angles, and alternate interior angles congruent, you can. But you'll have to write all those very long words about 20 times. Eventually, we hope that you'll just save yourself the effort, and think more critically about which angles you really need to prove congruent.