They were looking for the best ergonomics at the time. People operating terminal keyboards were usually very skilled typists. As a matter of fact, especially at the corporate level, they were being hired on that skill alone. And ergonomics was essential for fast and error-free data input. Keyboards were actually separately design for different purposes. Many layouts were being explored back in the 60s and 70s. IBM was probably the one taking the lead on this. But once rapid-data-entry software started becoming more available, around the concept of fields for data and navigation, eventually we settled with the iconic numeric keypad of today with a single key to switch for the index finger to swap between numeric data entry and field navigation. On many corp software at the time for financial management and calculation, you could fly through a screen with a single hand.