Why may a Canadian-controlled private corporation that earns business income of $100,000 in year 1 and $500,000

Question:

Why may a Canadian-controlled private that earns business income of $100,000 in year 1 and $500,000 in year 2 (total: $600,000) pay less tax than a earning $50,000 in year 1 and $550,000 in year 2 (total: $600,000)?
Corporation
A Corporation is a legal form of business that is separate from its owner. In other words, a corporation is a business or organization formed by a group of people, and its right and liabilities separate from those of the individuals involved. It may...