Maximize the flexibility. The entire program residing within the same institution also makes possible a greater flexibility of scheduling courses. No more, no less. The 150-hour degree meets the requirements for the CPA examinations and does not take the student beyond the minimum requirements. There is no skimping on content but the degree does leave ample opportunity for in-depth study of nonbusiness subjects right up to graduation.
Time is a scarce resource.
In fact, by taking one or possibly two courses each summer a student could complete the degree in four years. Financial aid is important. Some masters programs have scholarships, but most offer no financial assistance while usually charging a premium compared to undergraduate fees. In the current economics of higher education, private and public, this aspect of the 150-hour degree is important for many families. Graduate work in due season.