My guess (Just a guess because I can't read their mind) is the following:
Because the Information Views are built directly on normalized ECC tables, the developers found that most of the denormalization of the data would require the use of calculation views and their provided functionality. They then made the decision to build everything from calculation views for consistency.
My Thoughts:
I looked through most of the Hana Live ECC content and found that it would have been difficult to conform all of the tables into a standard multidimensional HANA model. (IE Attribute Views and Analytic Views only). With that said, there are still areas where they could have used Attribute Views. For example, KNA1_COM (Customers) and it's adjoining tables could have been conformed into a Customer Attribute View. The same could be said of CEPC (Profit Center) and many other calculation views. I guess in the end it did not matter because there are multiple calculated columns being used and most of the processing would have remained in the Calculation Engine regardless of which view type was used. I also noticed that some of the calculation views were configured to execute in the SQL Engine for better performance. This option only appears to be available in a Calculation View. The use of more Attribute Views would have been nice but only as it relates to auto-generated Universes in BOBJ 4.1.