Often, pin allocations are subject to the whim of the manufacturer - but it could be that a multiple pin connector could have different voltages on different pins.
Equipment could be designed with different power requirements and by using the one connector set, the manufacturer could save on the cost of these through bulk purchase. It would have the advantage that, if your device needed 12V and you had a supply for some other product that provided a number of voltages, but provided that voltage on the correct pin, it would still work.
Another possibility is that they got those connectors really cheap and just used them to do an undemanding job.