Its just another artifact of a system designed in the late 1700s. If you think about it, it makes sense for those times. A nomination back in the 18th and 19th century wouldn't necessarily be known to the Congress. So the questioning was relevant in those times in informing the Senate about the nomination and giving them the information they needed to make a choice. At least that would be the most optimistic interpretation. A more cynical interpretation would be that the confirmation hearing gives the nominee an opportunity in the 1800s to travel to Washington and try to make political deals with the power brokers.
Either way, the important takeaway is that it, like many procedural artifacts, was designed for a vastly different era without modern technology and were never updated. In the past the hearings were more "live" in that they did make a difference in how some voted.
EDIT: actually I was a little off. In the 1800s the nominee testifying wasn't typical of confirmation debates, often it was only outside witnesses who would testify.